<PAGE>
                                                                     Exhibit 4.4


                     Protection One Alarm Monitoring, Inc.,
                                    as Issuer

                              Protection One, Inc.,
                       Protection One International, Inc.,
                      Protection One Investments, Inc., and
                   Network Multi-Family Security Corporation,
                                  as Guarantors

               13 5/8% Senior Subordinated Discount Notes Due 2005

                                   ----------

                          Third Supplemental Indenture
                          dated as of February 14, 2000

                                       to

                       Indenture dated as of May 17, 1995

                                   ----------

                      State Street Bank and Trust Company,
                                   as Trustee
<PAGE>


           THIRD SUPPLEMENTAL INDENTURE dated as of February 14, 2000, by and
among PROTECTION ONE ALARM MONITORING, INC., a Delaware corporation
("Monitoring"), PROTECTION ONE, INC., a Delaware corporation (the "Parent
Company"), PROTECTION ONE INTERNATIONAL, INC., a Delaware corporation
("International"), PROTECTION ONE INVESTMENTS, INC., a Delaware corporation
("Investments"), NETWORK MULTI-FAMILY SECURITY CORPORATION, a Delaware
corporation ("Network", and together with the Parent Company, International,
Investments and Network, each a "Guarantor" and collectively, the "Guarantors"),
and STATE STREET BANK AND TRUST COMPANY, a Massachusetts trust company, as
successor trustee to The First National Bank of Boston under the Indenture
hereinafter referred to (the "Trustee"). All terms used herein and not otherwise
defined shall have the meanings ascribed thereto in the Indenture (as defined
below).

           WHEREAS, Monitoring, the Parent Company, Protection One Alarm
Services, Inc., an Oregon corporation ("Services"), A-Able Lock & Alarm, Inc., a
Nevada corporation ("A-Able"), and The First National Bank of Boston entered
into an Indenture dated as of May 17, 1995 (the "Indenture") providing for the
issuance by Monitoring of up to $166,000,000 aggregate principal amount 13 5/8%
Senior Subordinated Discount Notes due 2005 (the "Discount Notes");

           WHEREAS, in accordance with applicable provisions of the Indenture,
each of Services and A-Able was merged into Monitoring;

           WHEREAS, State Street Bank and Trust Company has acquired
substantially all of the corporate trust business of The First National Bank of
Boston and has thereby become successor trustee under the Indenture;

           WHEREAS, pursuant to Section 9.01 of the Indenture, Metrol Security
Services, Inc., a Delaware corporation ("Metrol"), Sonitrol of Arizona, Inc., an
Arizona corporation ("Sonitrol"), Monitoring, the Parent Company and the Trustee
thereafter entered into a First Supplemental Indenture dated as of July 26, 1996
for the purpose of adding Note Guarantees by Metrol and Sonitrol;

           WHEREAS, in accordance with applicable provisions of the Indenture,
Metrol and Sonitrol thereafter were merged into Monitoring;

           WHEREAS, pursuant to said Section 9.01, Security Holdings, Inc., a
Washington corporation ("Security Holdings"), Monitoring, the Parent Company and
the Trustee thereafter entered into a Second Supplemental Indenture dated as of
October 28,1996, for the purpose of adding a Note Guarantee by Security
Holdings;

           WHEREAS, in accordance with applicable provisions of the Indenture,
Security Holdings thereafter merged into Monitoring;

<PAGE>


           WHEREAS, Section 9.01 of the Indenture provides that Monitoring and
the Guarantors, in each case when authorized by a resolution of such company's
board of directors (or, in the case of a Guarantor, any committee of such
company's board of directors duly authorized to act under the Indenture), and
the Trustee, at any time and from time to time, may, without the consent of any
Holder, enter into an indenture supplemental to the Indenture for the purpose of
(i) reflecting that Security Holdings has ceased to be liable on its Note
Guarantee because it is no longer a Subsidiary of Monitoring and (ii) adding
Note Guarantees by International, Investments and Network;

           WHEREAS, Monitoring and the Guarantors desire to provide for a Note
Guarantee of payment of the Securities by International, Investments and
Network;

           WHEREAS, Monitoring and the Guarantors desire among other things to
amend the preamble of the Indenture to reflect the addition of International,
Investments and Network as Guarantors; and

           WHEREAS, all things necessary to make this Third Supplemental
Indenture a valid indenture supplement to the Indenture have been done;

           NOW, THEREFORE, THIS THIRD SUPPLEMENTAL INDENTURE WITNESSETH:

           For and in consideration of the premises, it is hereby mutually
covenanted and agreed, for the equal and proportionate benefit of all Holders of
the Notes, as follows:

                                    ARTICLE I

                           AMENDMENT OF THE INDENTURE

     A.   PREAMBLE. The preamble of the Indenture is hereby amended and restated
in its entirety to read as follows:

          "INDENTURE dated as of May 17, 1995 by and among PROTECTION ONE ALARM
     MONITORING, INC., a Delaware corporation ("Monitoring"), and PROTECTION
     ONE, INC., a Delaware corporation (the "Parent Company"), PROTECTION ONE
     INTERNATIONAL, INC., a Delaware corporation ("International"), PROTECTION
     ONE INVESTMENTS, INC., a Delaware corporation ("Investments"), NETWORK
     MULTI-FAMILY SECURITY CORPORATION, a Delaware corporation ("Network", and
     together with the Parent Company, International and Investments, the
     "Guarantors"), as Guarantors, and STATE STREET BANK AND TRUST COMPANY, a
     Massachusetts trust company, as trustee (the "Trustee")."

                                       2
<PAGE>

     B. NOTE GUARANTEES. Each of International, Investments and Network hereby
provides a Note Guarantee of payment of the Securities pursuant to Article
Eleven of the Indenture, and it is acknowledged that Security Holdings has
ceased to be liable on its Note Guarantee because it is no longer a Subsidiary
of Monitoring.

     C. REFERENCES TO GUARANTORS. Any reference in any Section of the Indenture
to the Guarantors or any of them shall be deemed to include International,
Investments and Network and exclude Security Holdings.

                                   ARTICLE II

                                  MISCELLANEOUS

     A. EXECUTION OF SUPPLEMENTAL INDENTURE. This Third Supplemental Indenture
is executed and shall be construed as an indenture supplemental to the Indenture
and, as provided in the Indenture, this Third Supplemental Indenture forms a
part thereof. The Indenture, as supplemented and amended by the First
Supplemental Indenture, the Second Supplemental Indenture and this Third
Supplemental Indenture, is in all respects hereby adopted, ratified and
confirmed and shall remain in full force and effect in accordance with its
terms.

     B. RESPONSIBILITY FOR RECITALS, ETC. The recitals herein shall be taken as
the statements of Monitoring and the Guarantors, and the Trustee assumes no
responsibility for the correctness thereof. The Trustee makes no representation
as to the validity or sufficiency of this Third Supplemental Indenture.

     C. PROVISIONS BINDING ON SUCCESSORS. All the covenants and agreements in
this Third Supplemental Indenture by Monitoring and the Guarantors shall bind
their respective successors and assigns whether so expressed or not.

     D. GOVERNING LAW. This Third Supplemental Indenture shall be governed by
the internal laws of the State of New York.

     E. EXECUTION AND COUNTERPARTS. This Third Supplemental Indenture may be
executed in any number of counterparts, each of which shall be an original but
such counterparts shall together constitute but one and the same instrument.

     F. EFFECTIVENESS. This Third Supplemental Indenture shall become effective
immediately upon its execution and delivery by Monitoring, each of the
Guarantors and the Trustee


                                       3
<PAGE>

                                   Signatures

           IN WITNESS WHEREOF, the parties hereto have caused this Third
Supplemental Indenture to be duly executed, all as of the date first written
above.

                                        PROTECTION ONE ALARM
                                        MONITORING, INC., as Issuer


                                        By:   /s/ Annette Beck
                                           ------------------------------------
                                              Annette Beck
                                              President

                                        PROTECTION ONE, INC., as Parent Company


                                        By:   /s/ Annette Beck
                                           ------------------------------------
                                              Annette Beck
                                              President


                                        PROTECTION ONE INTERNATIONAL, INC.


                                        By:   /s/ John E. Mack  III
                                           ------------------------------------
                                              John E. Mack, III
                                              President


                                        PROTECTION ONE INVESTMENTS, INC.


                                        By:   /s/ John E. Mack  III
                                           ------------------------------------
                                              John E. Mack, III
                                              President


                                        NETWORK MULTI-FAMILY SECURITY
                                        CORPORATION


                                        By:   /s/ Steven V. Williams
                                           ------------------------------------
                                              Steven V. Williams
                                              President

<PAGE>

                                        STATE STREET BANK AND TRUST COMPANY,
                                        as Trustee


                                        By:     /s/ Andrew M. Sinasky
                                           ------------------------------------
                                        Name:   Andrew M. Sinasky
                                             ----------------------------------
                                        Title:  Assistant Vice President
                                              ---------------------------------