<PAGE>   1
                                                                     EXHIBIT 4.9

                                REVOLVING NOTE(1)
                    

        $75,000,000                                            Chicago, Illinois
                                                                    June 7, 1996


                  FOR VALUE RECEIVED, the undersigned, Protection One Alarm
Monitoring, Inc., a Delaware corporation ("Borrower"), hereby unconditionally
promises to pay to the order of Heller Financial, Inc., a Delaware corporation
("Lender"), at the office of Agent (as defined in the Credit Agreement) at 500
West Monroe Street, Chicago, Illinois 60611, or at such other place as Agent may
from time to time designate in writing, in lawful money of the United States of
America and in immediately available funds, the principal sum of SEVENTY-FIVE
MILLION DOLLARS ($75,000,000) or, if less, the aggregate unpaid principal amount
of the Revolving Loan advanced by Lender pursuant to that certain Amended and
Restated Credit Agreement dated as of the date hereof among Borrower, Heller
Financial, Inc., as Agent and as Lender, and certain other Persons signatory
thereto, together with Heller, as Lenders (as the same may from time to time
hereafter be amended, supplemented, restated or modified, the "Credit
Agreement").

                  This Revolving Note is referred to in and was executed and
delivered pursuant to and evidences obligations of Borrower under the Credit
Agreement, to which reference is hereby made for a statement of the terms and
conditions under which the loans evidenced hereby are made and are to be repaid
and for a statement of Agent's and Lenders' remedies upon the occurrence of an
Event of Default as defined therein. The Credit Agreement is incorporated herein
by reference in its entirety. All capitalized terms used in this Revolving Note
shall have the meanings ascribed to them by the Credit Agreement, unless
otherwise defined herein.

                  This Revolving Note is secured pursuant to the Security
Agreement and the other Security Documents. Reference is made to the foregoing
documents for a statement of terms and conditions of such security.

                  This Revolving Note shall be paid in full as provided in the
Credit Agreement. Borrower further promises to pay interest, including default
interest, on the outstanding unpaid principal amount hereof, as provided in the
Credit Agreement. Interest shall be calculated on the basis of a three hundred
sixty (360) day year for the actual number of days elapsed.

                  If a payment hereunder becomes due and payable hereunder on a
day which is not a Business Day, the due date thereof shall be extended to the
next succeeding Business Day, and interest shall be payable thereon during such
extension at the applicable rate specified in the Credit Agreement. Credit for
payments made by Borrower shall, for the purpose of computing interest earned by
Lender, be given in accordance with the Credit Agreement.

                  In no event shall interest charged hereunder, however such
interest may be characterized or computed, exceed the highest rate permissible
under any law which a court of competent jurisdiction shall, in a final
determination, deem applicable hereto. In the event that such a court determines
that Lender has received interest hereunder in excess of the highest rate
applicable hereto, such excess interest shall be applied in accordance with the
term of the Credit Agreement.

                  Borrower hereby waives demand, presentment, protest, and
notice of demand, presentment, protest and nonpayment. Except for such notice as
may be specifically provided for in the Credit Agreement, Borrower also waives
all rights to notice and hearing of any kind prior to the exercise by Agent, on
behalf of


--------
(1) Notes in different principal amounts were executed by the Borrower in favor
    of each of the other "Lenders" under the Amended and Restated Credit 
    Agreement dated as of June 7, 1996.

                                        1
<PAGE>   2
Lenders, of the right to repossess the Collateral without judicial process or to
replevy, attach or levy upon the Collateral without notice or hearing.

                  In addition to and not in limitation of the foregoing and the
provisions of the Credit Agreement, Borrower further agrees, subject only to any
limitation imposed by applicable law, to pay all fees, costs and expenses,
including reasonable attorney's fees and legal expenses, incurred by the holder
of this Revolving Note in endeavoring to collect any amounts payable hereunder
which are not paid when due, whether by acceleration or otherwise.

                   THIS REVOLVING NOTE SHALL BE DEEMED TO HAVE BEEN DELIVERED
AND MADE AT CHICAGO, ILLINOIS AND SHALL BE INTERPRETED AND THE RIGHTS AND
LIABILITIES OF THE PARTIES HERETO DETERMINED IN ACCORDANCE WITH THE INTERNAL
LAWS (WITHOUT REGARD TO CONFLICT OF LAWS PROVISIONS) AND DECISIONS OF THE STATE
OF WHENEVER POSSIBLE EACH PROVISION OF THE REVOLVING NOTE SHALL BE INTERPRETED
IN SUCH MANNER AS TO BE EFFECTIVE AND VALID UNDER APPLICABLE LAW, BUT IF ANY
PROVISION OF THIS REVOLVING NOTE SHALL BE PROHIBITED BY OR INVALID UNDER
APPLICABLE LAW, SUCH PROVISION SHALL BE INEFFECTIVE TO THE EXTENT OF SUCH
PROHIBITION OR INVALIDITY, WITHOUT INVALIDATING THE REMAINDER OF SUCH PROVISION
OR THE REMAINING PROVISIONS OF THIS REVOLVING NOTE. WHENEVER IN THIS REVOLVING
NOTE REFERENCE IS MADE TO AGENT, ANY OF THE LENDERS OR BORROWER, SUCH REFERENCE
SHALL BE DEEMED TO INCLUDE, AS APPLICABLE, A REFERENCE TO THEIR RESPECTIVE
SUCCESSORS AND ASSIGNS. THE PROVISIONS OF THIS REVOLVING NOTE SHALL BE BINDING
UPON AND SHALL INURE TO THE BENEFIT OF SUCH SUCCESSORS AND ASSIGNS. THE
PROVISIONS OF THIS REVOLVING NOTE SHALL BE BINDING UPON AND SHALL INURE TO THE
BENEFIT OF SUCH SUCCESSORS AND ASSIGNS. BORROWER'S SUCCESSORS AND ASSIGNS SHALL
INCLUDE, WITHOUT LIMITATION, A RECEIVER, TRUSTEE OR DEBTOR-IN-POSSESSION OF OR
FOR BORROWER.

                  This Revolving Note supersedes, amends and restates the
revolving note (the "Existing Note") issued to Lender pursuant to the Existing
Credit Agreement. This Revolving Note is issued in substitution and replacement
of such Existing Note and not in payment thereof and any and all amounts
outstanding pursuant to such Existing Note shall be evidenced by this Revolving
Note and shall be paid in accordance with the terms hereof.

                  IN WITNESS WHEREOF, this Revolving Note has been duly executed
and delivered by Borrower as of the date first above written.

                                 PROTECTION ONE ALARM MONITORING, INC.


                                 By:               JOHN W. HESSE
                                        ___________________________________

                                 Title:            Executive Vice President
                                        ___________________________________


                                        2