<PAGE>

                                                                     Exhibit 3.6

                           CERTIFICATE OF AMENDMENT OF
              AMENDED AND RESTATED CERTIFICATE OF INCORPORATION OF
                        MACE SECURITY INTERNATIONAL, INC.

     MACE SECURITY INTERNATIONAL, INC., a corporation organized and existing
under and by virtue of the Delaware General Corporation Law (the "Corporation")
DOES HEREBY CERTIFY THAT:

     FIRST:  The name of the Corporation is "Mace Security International, Inc."

     SECOND: The Amended and Restated Certificate of Incorporation was filed by
             the Secretary of State on December 28, 1999.

     THIRD:  The Amended and Restated Certificate of Incorporation is hereby
             amended to effect a one-for-two reverse stock split of the issued
             and outstanding Common Stock.

     FOURTH: To accomplish the foregoing amendment, a new paragraph to Article
             FOURTH of the Amended and Restated Certificate of Incorporation
             shall be added as follows and as paragraph 4(c) thereunder:

     "As of December 17, 2002 at 12:01 AM Eastern Standard Time (the "Effective
     Date"), each two (2) shares of Common Stock of the corporation issued and
     outstanding immediately prior to the Effective Date (the "Old Common
     Stock") shall automatically be reclassified and continued, without any
     action on the part of the holder thereof, as one share of Common Stock (the
     "Reverse Split"). The Corporation shall not issue fractional shares on
     account of the Reverse Split. Holders of Old Common Stock who would
     otherwise be entitled to a fraction of a share on account of the Reverse
     Split shall receive, upon surrender of the stock certificates formally
     representing shares of the Old Common Stock, in lieu of such fractional
     share, an amount in cash (the "Cash-in-Lieu Amount") equal to the product
     of (i) the decimal remainder resulting from dividing the total number of
     shares of Old Common Stock held by two (2), which remainder is then
     multiplied by two (2), and (ii) the average of the closing price per share
     of the Old Common Stock on the ten (10) trading days immediately preceding
     the date that is five (5) days prior to the Effective Date or, if no such
     sale takes place on such days, the closing price per share on the next
     prior day on which a sale took place, in each case as reported in the Wall
     Street Journal. No interest shall be payable on the Cash-in-Lieu Amount."

     FIFTH:  The foregoing amendment was adopted by the directors and
             stockholders of the Corporation at duly called meetings of the
             board and stockholders, respectively, in accordance with the
             provisions of Section 242 of the Delaware General Corporation Law.

     IN WITNESS WHEREOF, the Corporation has caused this Certificate of
Amendment of Amended and Restated Certificate of Incorporation to be executed by
a duly authorized officer of the Corporation this 16th day of December, 2002.

                                      Mace Security International, Inc.

                                      /s/ Robert M. Kramer

                                      Robert M. Kramer
                                      Secretary, Executive Vice President