Exhibit 10.15

                  AMENDMENT TO AFFILIATE REGISTRATION AGREEMENT

     This Amendment (the "Amendment") is executed on and entered into as of
November 10, 1994 among AV Alarm, Inc., a Texas corporation (the "Company") and
James R. Hull (the "Shareholder").

                                    Recitals:

     The Company and the Shareholder have entered into an Affiliate Registration
Agreement (the "Registration Agreement") dated as of October 21, 1994. The
Company desires to enter into Warrant Agreement (the "Warrant Agreement") with
Heller Financial, Inc., a Delaware corporation ("Heller"). The Company desires
to grant certain registration rights to the holders of warrants granted pursuant
to the Warrant Agreement. The Company and the Shareholder desire to amend
certain provisions in the Registration Agreement.

     The parties agree as follows:

     1. Amendments. Paragraphs 1(c) and 1(d) of the Registration Agreement are
hereby amended to read in its entirety as follows:

               "(c) Priority on Primary Registrations. If a Piggyback
          Registration relates to an underwritten public offering of equity
          securities by the Company and the managing underwriters advise the
          Company in writing that in their opinion the number of securities
          requested to be included in such registration exceeds the number which
          can be sold in an orderly manner in such offering within a price range
          acceptable to the Company, the Company will include in such
          registration (i) first, the securities proposed to be sold by the
          Company, (ii) second, the Issued Warrant Shares (as defined in the
          Warrant Agreement), (iii) third, the Underlying Common Stock requested
          to be included in such registration, pro rata among the holders of
          such Underlying Common Stock on the basis of the number of shares
          owned by each such holder, (iv) fourth, securities other than
          Underlying Common Stock requested to be included in such registration
          by holders of Underlying Common Stock and non-Purchaser Affiliates,
          and (v) fifth, other securities requested to be included in such
          registration.

               (d) Priority on Secondary Registrations. If a Piggyback
          Registration relates to an underwritten public offering of equity
          securities by holders of the Company's securities and the managing
          underwriters advise the Company in writing that in their opinion the
          number of securities requested to be included in such registration
          exceeds the number which can be sold in an orderly manner in such
          offering within a price range acceptable to the holders initially
          requesting such registration, the Company will include in such
          registration (i) first, the Issued Warrant Shares, (ii) second, the
          securities requested to be included therein by the holders requesting
          such registration, (iii) third, the Underlying Common Stock requested
          to be included in such registration, pro rata among the holders of
          such Underlying Common Stock on the basis of the number of shares
          owned by each such holder, (iv) fourth, securities other than
          Underlying Common Stock




          requested to be included in such registration by holders of Underlying
          Common Stock and non-Purchaser Affiliates, and (v) fifth, other
          securities requested to be included in such registration."

All other provisions of the Registration Agreement shall remain in full force
and effect and shall not be deemed altered or amended by reason of any provision
of this Amendment.

     2. Miscellaneous.

     (a) Descriptive Headings. The descriptive headings of this Amendment are
inserted for convenience only and do not constitute a part of this Amendment.

     (b) Governing Law. The construction, validity and interpretation of this
Amendment will be governed by and construed in accordance with the domestic laws
of the State of Texas, without giving effect to any choice of law or conflict of
law provision or rule (whether of the State of Texas or any other jurisdiction)
that would cause the application of the laws of any jurisdiction other than the
State of Texas.

Counterparts. This Amendment may be executed in any number of counterparts and
by different parties hereto in separate counterparts, with the same effect as if
all parties had signed the same document. All such counterparts shall be deemed
an original, shall be construed together and shall constitute one and the same
instrument.

                                      * * *

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                                        COMPANY:

                                        AV Alarm, Inc.


                                        By: /s/ James R. Hull
                                            ------------------------------------
                                            James R. Hull,
                                            President

                                        PURCHASERS:

                                        Austin Ventures III-A, L.P.


                                        By AV Partners III, L.P.
                                        Its General Partner


                                        By:
                                            ------------------------------------
                                            Blaine F. Wesner,
                                            Authorized Signatory


                                        Austin Ventures III-B, L.P.


                                        By AV Partners III, L.P.
                                        Its General Partner


                                        By:
                                            ------------------------------------
                                            Blaine F. Wesner,
                                            Authorized Signatory

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                                                    COMPANY:

                                                    AV Alarm, Inc.


                                                    By:
                                                        ------------------------
                                                        James R. Hull,
                                                        President

                                                    PURCHASERS:

                                                    Austin Ventures III-A, L.P.

                                                    By AV Partners III, L.P.
                                                    Its General Partner


                                                    By: /s/ Blaine F. Wesner
                                                        ------------------------
                                                        Blaine F. Wesner,
                                                        Authorized Signatory

                                                    Austin Ventures III-B, L.P.

                                                    By AV Partners III, L.P.
                                                    Its General Partner


                                                    By: /s/ Blaine F. Wesner
                                                        ------------------------
                                                        Blaine F. Wesner,
                                                        Authorized Signatory

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