<PAGE>   1

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION

                              Washington, DC 20549
                                   FORM 10-K/A

[X]     Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange
        Act of 1934 for the Fiscal Year ended December 31, 1996
                                       OR
[ ]     Transition Report Pursuant to Section 13 or 15(d) of the Securities 
        Exchange Act of 1934

                          Commission file number 0-6272
                                   DATUM INC.
             (Exact name of Registrant as specified in its charter)

              Delaware                            95-2512237
       (State or other jurisdiction               (I.R.S. Employer
       of incorporation or organization)          Identification No.)

                    9975 Toledo Way, Irvine, California 92718
                    (Address of principal executive offices)
       Registrant's telephone number, including area code: (714) 380-8880

          Securities registered pursuant to Section 12(b) of the Act:

     Title of each class               Name of each exchange on which registered
     -------------------               -----------------------------------------
            None                                        None

           Securities registered pursuant to Section 12(g) of the Act:
                                  COMMON STOCK
                                (Title of Class)
                           ---------------------------

Indicate by check mark whether the Registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the Registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days.

Yes    X       No 
    -------       -------

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [X]

The aggregate market value of the voting stock held by non-affiliates of the
Registrant, based upon the closing sales price of the Common Stock as of April
18,1997, was approximately $67,936,794.

The number of outstanding shares of the Registrant's Common Stock as of April
18, 1997 was 5,171,130.


                       DOCUMENTS INCORPORATED BY REFERENCE

None.



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                                     PART IV


Item 14.    EXHIBITS, FINANCIAL STATEMENT SCHEDULES, AND REPORTS ON FORM 8-K.

(a)         The following documents are filed as part of this report:

      (3)   Exhibits

            The list of exhibits on the accompanying Exhibit Index is herein
            incorporated by reference.







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                                   SIGNATURES


Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Registrant has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized, at Irvine, California this
27th day of May, 1997.

                                                   DATUM INC.


                                                   By   Louis B. Horwitz
                                                     ---------------------------
                                                        Louis B. Horwitz
                                                        President and Director


Pursuant to the requirements of the Securities Exchange Act of 1934, this report
has been signed below by the following persons on behalf of the registrant and
in the capacities and on the date indicated.

<TABLE>
<CAPTION>
<S>                                       <C>                                    <C> 
 /s/ Louis B. Horwitz                     President and Director                 May 27, 1997
-----------------------------
Louis B. Horwitz                          (Principal Executive Officer)

 /s/ David A. Young                       Chief Financial Officer                May 27, 1997
-----------------------------
David A. Young                            (Principal Financial and Accounting
                                           Officer)

 /s/    *                                 Director                               May 27, 1997
-----------------------------
G. Tilton Gardner

 /s/    *                                 Director                               May 27, 1997
-----------------------------
Dan L. McGurk

 /s/    *                                 Director                               May 27, 1997
-----------------------------
Edward A. Money

 /s/    *                                 Director                               May 27, 1997
-----------------------------
Thomas J. O'Rourke

 /s/    *                                 Director                               May 27, 1997
-----------------------------
Michael M. Mann

 /s/    *                                 Director                               May 27, 1997
-----------------------------
R. David Hoover

 /s/    *                                 Director                               May 27, 1997
-----------------------------
Donovan B. Hicks
</TABLE>



*       By: David A. Young
            ------------------------------------
            David A. Young, Attorney-in-Fact




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<TABLE>
<CAPTION>

                                  EXHIBIT INDEX

EXHIBIT
NUMBER                        DESCRIPTION
------                        -----------

<S>               <C>                                                 
23.1              Consent of Independent Accountants
</TABLE>






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