<PAGE>
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 19, 1996
 
                                                   REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------
 
                                    FORM S-8
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------
 
                           CELLNET DATA SYSTEMS, INC.
             (Exact name of Registrant as specified in its charter)
 
                DELAWARE                                94-2951096
        (State of incorporation)           (I.R.S. Employer Identification No.)
 
                               125 SHOREWAY ROAD
                              SAN CARLOS, CA 94070
   (Address, including zip code, of Registrant's principal executive offices)
                            ------------------------
 
                           1992 INCENTIVE STOCK PLAN
                                1994 STOCK PLAN
                       1996 EMPLOYEE STOCK PURCHASE PLAN
                            (Full title of the plan)
                            ------------------------
 
                                 JOHN M. SEIDL
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           CELLNET DATA SYSTEMS, INC.
                               125 SHOREWAY ROAD
                              SAN CARLOS, CA 94070
                                 (415) 508-6000
(Name, address, and telephone number, including area code, of agent for service)
                            ------------------------
 
                                    COPY TO:
                            TREVOR J. CHAPLICK, ESQ.
                       WILSON, SONSINI, GOODRICH & ROSATI
                            PROFESSIONAL CORPORATION
                               650 PAGE MILL ROAD
                              PALO ALTO, CA 94304
                                 (415) 493-9300
 
                            ------------------------
 
                        CALCULATION OF REGISTRATION FEE
 
<TABLE>
<CAPTION>
                                                                  PROPOSED MAXIMUM    PROPOSED MAXIMUM
          TITLE OF EACH CLASS OF                AMOUNT TO BE       OFFERING PRICE        AGGREGATE            AMOUNT OF
        SECURITIES TO BE REGISTERED              REGISTERED          PER SHARE         OFFERING PRICE     REGISTRATION FEE
<S>                                          <C>                 <C>                 <C>                 <C>
Common Stock $.001 par value...............   4,190,478 shares      $   4.2386(1)      $ 17,761,760(1)        $   5,383
Common Stock $.001 par value...............   1,200,000 shares      $   11.951(2)      $ 14,341,200(2)        $   4,346
</TABLE>
 
(1) Estimated pursuant to Rule 457 solely for the purpose of calculating the
    registration fee on the basis, as to an aggregate of 4,190,478 shares, of
    100% of the average of the high and low prices reported in the NASDAQ
    National Market System on November 12, 1996.
 
(2) Estimated pursuant to Rule 457 solely for the purpose of calculating the
    registration fee on the basis, as to an aggregate of 1,200,000 shares, of
    85% of the average of the high and low prices reported in the NASDAQ
    National Market System on November 12, 1996.
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
                           CELLNET DATA SYSTEMS, INC.
                       REGISTRATION STATEMENT ON FORM S-8
                                    PART II
                 INFORMATION REQUIRED IN REGISTRATION STATEMENT
 
ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE
 
    There are hereby incorporated by reference in this Registration Statement
the following documents and information heretofore filed by CellNet Data
Systems, Inc. (the "Company") with the Securities and Exchange Commission:
 
    (1) The description of the Company's Common Stock contained in the Company's
Registration Statement on Form 8-A filed on September 26, 1996.
 
    (2) The Company's Quarterly Report on Form 10-Q for the fiscal quarter ended
September 30, 1996 filed on November 14, 1996.
 
    All documents filed by the Company pursuant to Sections 13(a), 13(c), 14 and
15(d) of the Securities Exchange Act of 1934 (the "1934 Act") on or after the
date of this Registration Statement and prior to the filing of a post-effective
amendment which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents.
 
ITEM 4.  DESCRIPTION OF SECURITIES.
 
    Not applicable.
 
ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.
 
    On the filing date of this Registration Statement, certain members of
counsel to the Registrant, Wilson Sonsini Goodrich & Rosati, Professional
Corporation and investment partnerships of which such persons are partners,
beneficially own 23,428 shares of the Company's Common Stock.
 
ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
    Section 145 of the Delaware General Corporation Law authorizes a court to
award, or a corporation's Board of Directors to grant, indemnity to directors
and officers in terms sufficiently broad to permit such indemnification under
certain circumstances for liabilities (including reimbursement for expenses
incurred) arising under the Securities Act of 1933, as amended (the "Securities
Act"). Further, in accordance with the Delaware General Corporation Law, the
Company's Restated Certificate of Incorporation provides for the indemnification
of directors to the fullest extent permissable under Delaware law. Article 6 of
the Bylaws of the Company provides for indemnification of officers, directors,
employees and certain agents to the maximum extent permitted by the Delaware
General Corporation Law. Persons covered by this indemnification provision
include any current or former directors, officers, employees and other agents of
the Company, as well as persons who serve at the request of the Company as
directors, officers, employees or agents of another enterprise.
 
    In addition, the Company has entered into contractual agreements with
certain directors and officers of the Company designated by the Board to
indemnify such individuals to the full extent permitted by law. These agreements
also resolve certain procedural and substantive matters that are not covered, or
are covered in less detail, in the Bylaws or by the Delaware General Corporation
Law.
 
                                      II-1
<PAGE>
    Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
registrant pursuant to the Delaware General Corporation Law, the Company's
Certificate of Incorporation, the foregoing Bylaw provisions or the Company's
indemnification agreements, the Company has been informed that in the opinion of
the Securities and Exchange Commission such indemnification is against public
policy as expressed in the Securities Act and is therefore unenforceable. In the
event that a claim for indemnification against such liabilities (other than the
payment by the Company of expenses incurred or paid by a director, officer or
controlling person of the Company in a successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered hereunder, the Company will,
unless in the opinion of its counsel the question has already been settled by
controlling precedent, submit to a court of appropriate jurisdiction the
question whether such indemnification by it is against public policy as
expressed in the Securities Act and will be governed by the final adjudication
of such issue.
 
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
    Not applicable.
 
ITEM 8.  EXHIBITS.
 
<TABLE>
<CAPTION>
EXHIBIT
NUMBER   DESCRIPTION
------   ----------------------------------------------------------------------
<C>      <S>
    4.1  1992 Incentive Stock Plan.
 
    4.2  1994 Stock Plan.
 
    4.3  1996 Employee Stock Purchase Plan.
 
    5.1  Opinion of counsel as to legality of securities being registered (see
           page II-7).
 
   23.1  Consent of counsel (contained in Exhibit 5.1).
 
   23.2  Independent Auditors' Consent (see page II-8).
 
   24.1  Power of Attorney (see pages II-5 and II-6 of the Registration
           Statement).
 
   99.1  Consolidated Financial Statements.
</TABLE>
 
ITEM 9.  UNDERTAKINGS.
 
    A. The undersigned registrant hereby undertakes:
 
        (1) To file, during any period in which offers or sales are being made,
    a post-effective amendment to this registration statement to include any
    material information with respect to the plan of distribution not previously
    disclosed in the registration statement or any material change to such
    information in the registration statement.
 
        (2) That, for the purpose of determining any liability under the
    Securities Act, each such post-effective amendment shall be deemed to be a
    new registration statement relating to the securities offered therein, and
    the offering of such securities at that time shall be deemed to be the
    initial bona fide offering thereof.
 
        (3) To remove from registration by means of a post-effective amendment
    any of the securities being registered which remain unsold at the
    termination of the offering.
 
    B.  The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
registrant's annual report pursuant to section 13(a) or
 
                                      II-2
<PAGE>
section 15(d) of the Securities Exchange Act of 1934 (and, where applicable,
each filing of an employee benefit plan's annual report pursuant to section
15(d) of the Securities Exchange Act of 1934) that is incorporated by reference
in the registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.
 
    C.  Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
registrant pursuant to the foregoing provisions, or otherwise, the registrant
has been advised that in the opinion of the Securities and Exchange Commission
such indemnification is against public policy as expressed in the Securities Act
and is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the registrant of expenses
incurred or paid by a director, officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
 
                                      II-3
<PAGE>
                                   SIGNATURES
 
    Pursuant to the requirements of the Securities Act, the registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this registration statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the City
of San Carlos, State of California, on November 15, 1996.
 
                                CELLNET DATA SYSTEMS, INC.
 
                                By:               /s/ JOHN M. SEIDL
                                      -----------------------------------------
                                                    John M. Seidl
                                        PRESIDENT AND CHIEF EXECUTIVE OFFICER
 
                                      II-4
<PAGE>
                               POWER OF ATTORNEY
 
    KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Paul G. Manca and David L. Perry and each of
them, as his attorney-in-fact, with full power of substitution in each, for him
in any and all capacities to sign any amendments to this Registration Statement
on Form S-8, and to file the same, with exhibits thereto and other documents in
connection therewith, with the Securities and Exchange Commission, hereby
ratifying and confirming all that said attorney-in-fact, or his substitutes, may
do or cause to be done by virtue hereof.
 
    Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed below by the following persons in the
capacities and on the dates indicated.
 
<TABLE>
<CAPTION>
          SIGNATURE                      CAPACITY                  DATE
------------------------------  --------------------------  -------------------
<C>                             <S>                         <C>
 
                                President, Chief Executive
      /s/ JOHN M. SEIDL           Officer (Principal
------------------------------    Executive Officer) and     November 15, 1996
        John M. Seidl             Director
 
                                Senior Vice President of
      /s/ PAUL G. MANCA           Finance and Chief
------------------------------    Financial Officer          November 15, 1996
        Paul G. Manca             (Principal Financial and
                                  Accounting Officer)
 
       /s/ PAUL M. COOK
------------------------------  Director                     November 15, 1996
         Paul M. Cook
 
     /s/ NEAL M. DOUGLAS
------------------------------  Director                     November 15, 1996
       Neal M. Douglas
 
    /s/ WILLIAM C. EDWARDS
------------------------------  Director                     November 15, 1996
      William C. Edwards
 
       /s/ WILLIAM HART
------------------------------  Director                     November 15, 1996
         William Hart
 
       /s/ BRIAN KWAIT
------------------------------  Director                     November 15, 1996
         Brian Kwait
 
      /s/ NANCY E. PFUND
------------------------------  Director                     November 15, 1996
        Nancy E. Pfund
</TABLE>
 
                                      II-5
<PAGE>
<TABLE>
<CAPTION>
          SIGNATURE                      CAPACITY                  DATE
------------------------------  --------------------------  -------------------
<C>                             <S>                         <C>
      /s/ PAUL J. SALEM
------------------------------  Director                     November 15, 1996
        Paul J. Salem
 
     /s/ HENRY B. SARGENT
------------------------------  Director                     November 15, 1996
       Henry B. Sargent
</TABLE>
 
                                      II-6
<PAGE>
                                                                     EXHIBIT 5.1
 
                               November 15, 1996
 
CellNet Data Systems, Inc.
125 Shoreway Road
San Carlos, CA 94070
 
       RE: REGISTRATION STATEMENT ON FORM S-8
 
Gentlemen:
 
    We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on or about November 13, 1996 (the
"Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of 6,000,000 post-split shares of your
Common Stock which are to be issued pursuant to the 1992 Stock Option Plan,
3,000,000 post-split shares of your Common Stock which are to be issued pursuant
to the 1994 Stock Plan and 1,200,000 post-split shares of your Common Stock
(collectively, the "Shares") which are to be issued pursuant to the 1996
Employee Stock Purchase Plan (collectively, the "Plans"). As your legal counsel,
we have examined the proceedings taken and are familiar with the proceedings
proposed to be taken by you in connection with the sale and issuance of the
Shares under the Plans.
 
    It is our opinion that, when issued and sold in the manner referred to in
the Plans and pursuant to the agreements which accompany the Plans, the Shares
will be legally and validly issued, fully paid and nonassessable.
 
    We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement, including any Prospectus constituting a part thereof,
and any amendments thereto.
 
                             Sincerely yours,
                             WILSON SONSINI GOODRICH & ROSATI
                             Professional Corporation
 
                             /s/Wilson Sonsini Goodrich & Rosati, P.C.
 
                                      II-7
<PAGE>
                                                                    EXHIBIT 23.2
 
                         INDEPENDENT AUDITORS' CONSENT
 
    We consent to the use in this Registration Statement of CellNet Data
Systems, Inc. on Form S-8 of our report dated February 9, 1996 (April 11, 1996,
as to the last sentence of the second paragraph of Note 5 and October 31, 1996
as to Note 10), appearing in Exhibit 99.1, which is part of this Registration
Statement.
 
DELOITTE & TOUCHE LLP
 
San Jose, California
November 13, 1996
 
                                      II-8
<PAGE>
                               INDEX TO EXHIBITS
 
<TABLE>
<CAPTION>
EXHIBIT
 NUMBER                                 DESCRIPTION
--------   ----------------------------------------------------------------------
<C>        <S>                                                                     <C>
      4.1  1992 Incentive Stock Plan
 
      4.2  1994 Stock Plan
 
      4.3  1996 Employee Stock Purchase Plan
 
      5.1  Opinion of Counsel as to legality of securities being registered (see
             page II-7 of the Registration Statement).
 
     23.1  Consent of Counsel (contained in Exhibit 5.1 hereto).
 
     23.2  Independent Auditors' Consent (see page II-8 of the Registration
             Statement).
 
     24.1  Power of Attorney (see pages II-5 and II-6 of the Registration
             Statement).
 
     99.1  Consolidated Financial Statements
</TABLE>
[{"type": "S-8", "sequence": "1", "description": "S-8", "secsgml_size_bytes": 19190}]
{"company-data": {"conformed-name": "CELLNET DATA SYSTEMS INC", "cik": "0000805956", "assigned-sic": "4822", "irs-number": "942951096", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-16399", "film-number": "96669240"}, "business-address": {"street1": "125 SHOREWAY ROAD", "city": "SAN CARLOS", "state": "CA", "zip": "94070", "phone": "4154939300"}, "mail-address": {"street1": "125 SHOREWAY ROAD", "city": "SAN CARLOS", "state": "CA", "zip": "94070"}}
AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 19, 1996
 
                                                   REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------
 
                                    FORM S-8
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------
 
                           CELLNET DATA SYSTEMS, INC.
             (Exact name of Registrant as specified in its charter)
 
                DELAWARE                                94-2951096
        (State of incorporation)           (I.R.S. Employer Identification No.)
 
                               125 SHOREWAY ROAD
                              SAN CARLOS, CA 94070
   (Address, including zip code, of Registrant's principal executive offices)
                            ------------------------
 
                           1992 INCENTIVE STOCK PLAN
                                1994 STOCK PLAN
                       1996 EMPLOYEE STOCK PURCHASE PLAN
                            (Full title of the plan)
                            ------------------------
 
                                 JOHN M. SEIDL
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           CELLNET DATA SYSTEMS, INC.
                               125 SHOREWAY ROAD
                              SAN CARLOS, CA 94070
                                 (415) 508-6000
(Name, address, and telephone number, including area code, of agent for service)
                            ------------------------
 
                                    COPY TO:
                            TREVOR J. CHAPLICK, ESQ.
                       WILSON, SONSINI, GOODRICH & ROSATI
                            PROFESSIONAL CORPORATION
                               650 PAGE MILL ROAD
                              PALO ALTO, CA 94304
                                 (415) 493-9300
 
                            ------------------------
 
                        CALCULATION OF REGISTRATION FEE
PROPOSED MAXIMUM    PROPOSED MAXIMUM
          TITLE OF EACH CLASS OF                AMOUNT TO BE       OFFERING PRICE        AGGREGATE            AMOUNT OF
        SECURITIES TO BE REGISTERED              REGISTERED          PER SHARE         OFFERING PRICE     REGISTRATION FEE
Common Stock $.001 par value...............   4,190,478 shares      $   4.2386(1)      $ 17,761,760(1)        $   5,383
Common Stock $.001 par value...............   1,200,000 shares      $   11.951(2)      $ 14,341,200(2)        $   4,346
(1) Estimated pursuant to Rule 457 solely for the purpose of calculating the
    registration fee on the basis, as to an aggregate of 4,190,478 shares, of
    100% of the average of the high and low prices reported in the NASDAQ
    National Market System on November 12, 1996.
 
(2) Estimated pursuant to Rule 457 solely for the purpose of calculating the
    registration fee on the basis, as to an aggregate of 1,200,000 shares, of
    85% of the average of the high and low prices reported in the NASDAQ
    National Market System on November 12, 1996.
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
CELLNET DATA SYSTEMS, INC.
                       REGISTRATION STATEMENT ON FORM S-8
                                    PART II
                 INFORMATION REQUIRED IN REGISTRATION STATEMENT
 
ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE
 
    There are hereby incorporated by reference in this Registration Statement
the following documents and information heretofore filed by CellNet Data
Systems, Inc. (the "Company") with the Securities and Exchange Commission:
 
    (1) The description of the Company's Common Stock contained in the Company's
Registration Statement on Form 8-A filed on September 26, 1996.
 
    (2) The Company's Quarterly Report on Form 10-Q for the fiscal quarter ended
September 30, 1996 filed on November 14, 1996.
 
    All documents filed by the Company pursuant to Sections 13(a), 13(c), 14 and
15(d) of the Securities Exchange Act of 1934 (the "1934 Act") on or after the
date of this Registration Statement and prior to the filing of a post-effective
amendment which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold shall be deemed to be
incorporated by reference in this Registration Statement and to be part hereof
from the date of filing of such documents.
 
ITEM 4.  DESCRIPTION OF SECURITIES.
 
    Not applicable.
 
ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.
 
    On the filing date of this Registration Statement, certain members of
counsel to the Registrant, Wilson Sonsini Goodrich & Rosati, Professional
Corporation and investment partnerships of which such persons are partners,
beneficially own 23,428 shares of the Company's Common Stock.
 
ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
    Section 145 of the Delaware General Corporation Law authorizes a court to
award, or a corporation's Board of Directors to grant, indemnity to directors
and officers in terms sufficiently broad to permit such indemnification under
certain circumstances for liabilities (including reimbursement for expenses
incurred) arising under the Securities Act of 1933, as amended (the "Securities
Act"). Further, in accordance with the Delaware General Corporation Law, the
Company's Restated Certificate of Incorporation provides for the indemnification
of directors to the fullest extent permissable under Delaware law. Article 6 of
the Bylaws of the Company provides for indemnification of officers, directors,
employees and certain agents to the maximum extent permitted by the Delaware
General Corporation Law. Persons covered by this indemnification provision
include any current or former directors, officers, employees and other agents of
the Company, as well as persons who serve at the request of the Company as
directors, officers, employees or agents of another enterprise.
 
    In addition, the Company has entered into contractual agreements with
certain directors and officers of the Company designated by the Board to
indemnify such individuals to the full extent permitted by law. These agreements
also resolve certain procedural and substantive matters that are not covered, or
are covered in less detail, in the Bylaws or by the Delaware General Corporation
Law.
 
                                      II-1
Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
registrant pursuant to the Delaware General Corporation Law, the Company's
Certificate of Incorporation, the foregoing Bylaw provisions or the Company's
indemnification agreements, the Company has been informed that in the opinion of
the Securities and Exchange Commission such indemnification is against public
policy as expressed in the Securities Act and is therefore unenforceable. In the
event that a claim for indemnification against such liabilities (other than the
payment by the Company of expenses incurred or paid by a director, officer or
controlling person of the Company in a successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered hereunder, the Company will,
unless in the opinion of its counsel the question has already been settled by
controlling precedent, submit to a court of appropriate jurisdiction the
question whether such indemnification by it is against public policy as
expressed in the Securities Act and will be governed by the final adjudication
of such issue.
 
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
    Not applicable.
 
ITEM 8.  EXHIBITS.
EXHIBIT
NUMBER   DESCRIPTION
------   ----------------------------------------------------------------------
4.1  1992 Incentive Stock Plan.
 
    4.2  1994 Stock Plan.
 
    4.3  1996 Employee Stock Purchase Plan.
 
    5.1  Opinion of counsel as to legality of securities being registered (see
           page II-7).
 
   23.1  Consent of counsel (contained in Exhibit 5.1).
 
   23.2  Independent Auditors' Consent (see page II-8).
 
   24.1  Power of Attorney (see pages II-5 and II-6 of the Registration
           Statement).
 
   99.1  Consolidated Financial Statements.
ITEM 9.  UNDERTAKINGS.
 
    A. The undersigned registrant hereby undertakes:
 
        (1) To file, during any period in which offers or sales are being made,
    a post-effective amendment to this registration statement to include any
    material information with respect to the plan of distribution not previously
    disclosed in the registration statement or any material change to such
    information in the registration statement.
 
        (2) That, for the purpose of determining any liability under the
    Securities Act, each such post-effective amendment shall be deemed to be a
    new registration statement relating to the securities offered therein, and
    the offering of such securities at that time shall be deemed to be the
    initial bona fide offering thereof.
 
        (3) To remove from registration by means of a post-effective amendment
    any of the securities being registered which remain unsold at the
    termination of the offering.
 
    B.  The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
registrant's annual report pursuant to section 13(a) or
 
                                      II-2
section 15(d) of the Securities Exchange Act of 1934 (and, where applicable,
each filing of an employee benefit plan's annual report pursuant to section
15(d) of the Securities Exchange Act of 1934) that is incorporated by reference
in the registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.
 
    C.  Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
registrant pursuant to the foregoing provisions, or otherwise, the registrant
has been advised that in the opinion of the Securities and Exchange Commission
such indemnification is against public policy as expressed in the Securities Act
and is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the registrant of expenses
incurred or paid by a director, officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
 
                                      II-3
SIGNATURES
 
    Pursuant to the requirements of the Securities Act, the registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this registration statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the City
of San Carlos, State of California, on November 15, 1996.
 
                                CELLNET DATA SYSTEMS, INC.
 
                                By:               /s/ JOHN M. SEIDL
                                      -----------------------------------------
                                                    John M. Seidl
                                        PRESIDENT AND CHIEF EXECUTIVE OFFICER
 
                                      II-4
POWER OF ATTORNEY
 
    KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Paul G. Manca and David L. Perry and each of
them, as his attorney-in-fact, with full power of substitution in each, for him
in any and all capacities to sign any amendments to this Registration Statement
on Form S-8, and to file the same, with exhibits thereto and other documents in
connection therewith, with the Securities and Exchange Commission, hereby
ratifying and confirming all that said attorney-in-fact, or his substitutes, may
do or cause to be done by virtue hereof.
 
    Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed below by the following persons in the
capacities and on the dates indicated.
SIGNATURE                      CAPACITY                  DATE
------------------------------  --------------------------  -------------------
President, Chief Executive
      /s/ JOHN M. SEIDL           Officer (Principal
------------------------------    Executive Officer) and     November 15, 1996
        John M. Seidl             Director
 
                                Senior Vice President of
      /s/ PAUL G. MANCA           Finance and Chief
------------------------------    Financial Officer          November 15, 1996
        Paul G. Manca             (Principal Financial and
                                  Accounting Officer)
 
       /s/ PAUL M. COOK
------------------------------  Director                     November 15, 1996
         Paul M. Cook
 
     /s/ NEAL M. DOUGLAS
------------------------------  Director                     November 15, 1996
       Neal M. Douglas
 
    /s/ WILLIAM C. EDWARDS
------------------------------  Director                     November 15, 1996
      William C. Edwards
 
       /s/ WILLIAM HART
------------------------------  Director                     November 15, 1996
         William Hart
 
       /s/ BRIAN KWAIT
------------------------------  Director                     November 15, 1996
         Brian Kwait
 
      /s/ NANCY E. PFUND
------------------------------  Director                     November 15, 1996
        Nancy E. Pfund
II-5
SIGNATURE                      CAPACITY                  DATE
------------------------------  --------------------------  -------------------
/s/ PAUL J. SALEM
------------------------------  Director                     November 15, 1996
        Paul J. Salem
 
     /s/ HENRY B. SARGENT
------------------------------  Director                     November 15, 1996
       Henry B. Sargent
II-6
EXHIBIT 5.1
 
                               November 15, 1996
 
CellNet Data Systems, Inc.
125 Shoreway Road
San Carlos, CA 94070
 
       RE: REGISTRATION STATEMENT ON FORM S-8
 
Gentlemen:
 
    We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on or about November 13, 1996 (the
"Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of 6,000,000 post-split shares of your
Common Stock which are to be issued pursuant to the 1992 Stock Option Plan,
3,000,000 post-split shares of your Common Stock which are to be issued pursuant
to the 1994 Stock Plan and 1,200,000 post-split shares of your Common Stock
(collectively, the "Shares") which are to be issued pursuant to the 1996
Employee Stock Purchase Plan (collectively, the "Plans"). As your legal counsel,
we have examined the proceedings taken and are familiar with the proceedings
proposed to be taken by you in connection with the sale and issuance of the
Shares under the Plans.
 
    It is our opinion that, when issued and sold in the manner referred to in
the Plans and pursuant to the agreements which accompany the Plans, the Shares
will be legally and validly issued, fully paid and nonassessable.
 
    We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement, including any Prospectus constituting a part thereof,
and any amendments thereto.
 
                             Sincerely yours,
                             WILSON SONSINI GOODRICH & ROSATI
                             Professional Corporation
 
                             /s/Wilson Sonsini Goodrich & Rosati, P.C.
 
                                      II-7
EXHIBIT 23.2
 
                         INDEPENDENT AUDITORS' CONSENT
 
    We consent to the use in this Registration Statement of CellNet Data
Systems, Inc. on Form S-8 of our report dated February 9, 1996 (April 11, 1996,
as to the last sentence of the second paragraph of Note 5 and October 31, 1996
as to Note 10), appearing in Exhibit 99.1, which is part of this Registration
Statement.
 
DELOITTE & TOUCHE LLP
 
San Jose, California
November 13, 1996
 
                                      II-8
INDEX TO EXHIBITS
EXHIBIT
 NUMBER                                 DESCRIPTION
--------   ----------------------------------------------------------------------
4.1  1992 Incentive Stock Plan
 
      4.2  1994 Stock Plan
 
      4.3  1996 Employee Stock Purchase Plan
 
      5.1  Opinion of Counsel as to legality of securities being registered (see
             page II-7 of the Registration Statement).
 
     23.1  Consent of Counsel (contained in Exhibit 5.1 hereto).
 
     23.2  Independent Auditors' Consent (see page II-8 of the Registration
             Statement).
 
     24.1  Power of Attorney (see pages II-5 and II-6 of the Registration
             Statement).
 
     99.1  Consolidated Financial Statements