FOURTH AMENDMENT TO THE LOAN AND SECURITY AGREEMENT

Fourth Amendment dated as of May 11, 2000
(this "Amendment") to the Loan and Security Agreement dated as of December 31,
1997 (as amended and modified, the "Loan Agreement"), among GENERAL
ELECTRIC CAPITAL CORPORATION, a New York corporation ("Lender") and
KNOGO NORTH AMERICA INC., a Delaware corporation ("Borrower") and
the other Credit Parties executing this Amendment.

WITNESSETH :

WHEREAS, Borrower has requested that
Lender amend the Loan Agreement to provide additional financial accommodations
to Borrower;

WHEREAS, Lender is willing to so amend
the Loan Agreement on the terms and conditions set forth herein;

NOW, THEREFORE, in consideration of the
premises, the covenants and agreements contained herein, and for other good and
valuable consideration, the receipt and adequacy of which are hereby
acknowledged, the parties do hereby agree that all capitalized terms used herein
shall have the meanings ascribed thereto in the Loan Agreement and do hereby
further agree as follows:

STATEMENT OF TERMS

1.   Amendment to Loan
Agreement. Subject to the satisfaction of conditions precedent set forth
in Section 3 of this Amendment, each Credit Party and Lender agree to amend the
Loan Agreement as follows:

| | (a)     Section 1.5 is amended as follows
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| | (i)  Section 1.5(a) is amended by inserting the following sentence at the end
thereof:
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| | Notwithstanding
the foregoing, Borrower shall pay interest to Lender on the aggregate
outstanding Revolving Credit Advances consisting of Special Advances at a
floating rate equal to the Index Rate plus five percent (5.00%) per annum (the
Special Advance Rate).
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| | (ii)  Section 1.5(d) is amended in its entirety to provide as follows:
thereof:
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| | (d)  
Effective upon the occurrence of any Event of Default and for so long as any
Event of Default shall be continuing, upon notice to the Borrower (except that
no notice shall be required upon the occurrence of any Event of Default
specified in Sections 7.1(e), (f) or (g)) the Revolving Credit Rate, the Special
Advance Rate and the Letter of Credit Fee shall automatically be increased by
two percentage points (2%) per annum (such increased rate, the Default
Rate), and all outstanding Obligations, including unpaid interest and
Letter of Credit Fees, shall continue to accrue interest from the date of such
Event of Default at the Default Rate applicable to such Obligations.
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| | (b)     Schedule A is amended as follows:
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| | (i)  the following defined
terms are inserted in the appropriate alphabetical order:
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| | Eligible
Unbilled Accounts shall mean those Accounts
which arise from the sale of goods but which require the installation of such
goods by Borrower or Video, which would otherwise constitute Eligible Accounts
except for the fact that the goods which have been delivered have not yet been
installed.
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| | Special
Advances shall mean those Revolving Credit
Advances in excess of the Borrowing Base with the Borrowing Base being
determined as if the Special Advance Amount was $0.
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| | Special Advance Rate shall have
the meaning assigned to it in Section 1.5(a).
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| | Fourth
Amendment shall mean the Fourth Amendment to
Loan and Security Agreement dated May 11, 2000 among Lender, Borrower and the
other Credit Parties.
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| | Fourth
Amendment Effective Date shall have the meaning
assigned to the term Effective Date in Fourth Amendment.
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| | (ii)  the following defined
term is amended in its entirety to provide as follows:
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| | Special
Advance Amount shall mean (a) for the period
commencing on the Fourth Amendment Effective Date and ending on September 1,
2000, the lesser of (i) $500,000 or (ii) 50% of the value (as determined by
Lender) of Eligible Unbilled Accounts of Borrower and Video and (b) at all other
times, $0.
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| | (c) | The Transaction Summary is amended to reflect the changes made in this
Amendment.
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2.   Representations and
Warranties. To induce Lender to enter into this Amendment, each
Credit Party hereto hereby warrants, represents and covenants to Lender that:
(a) each representation and warranty of the Credit Parties set forth in the Loan
Agreement is hereby restated and reaffirmed as true and correct on and as of the
date hereof after giving affect to this Amendment as if such representation or
warranty were made on and as of the date hereof (except to the extent that any
such representation or warranty expressly relates to a prior specific date or
period in which case it is true and correct as of such prior date or period),
and no Default or Event of Default has occurred and is continuing as of this
date under the Loan Agreement after giving effect to this Amendment; (b) each
Credit Party hereto has the power and is duly authorized to enter into, deliver
and perform this Amendment, and this Amendment is the legal, valid and binding
obligation of such Credit Party enforceable against it in accordance with its
terms; and (c) no later than thirty (30) days from the date of this Amendment,
Borrower shall deliver to Lender warrants to purchase 100,000 shares of the
common stock of Sentry at a closing price for the common stock on May 11, 2000,
on terms and conditions and pursuant to agreements satisfactory to Lender in all
respects and the failure to do so shall constitute an Event of Default under the
Loan Agreement.

3.   Conditions Precedent to Effectiveness of this Amendment. The effectiveness of
this Amendment is subject to the fulfillment of the following conditions
precedent:

| | (a) | Lender shall have received in form and substance satisfactory to it, one or more
counterparts of this Amendment duly executed and delivered by the Credit Parties
hereto;
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| | (b) | Any and all guarantors of the Obligations shall have consented to the execution,
delivery and performance of this Amendment and all of the transactions
contemplated hereby by signing one or more counterparts of this Amendment in the
appropriate space indicated below and returning same to Lender; and
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| | (c) | Borrower shall have paid to Lender all of Lenders legal fees, costs and expenses
incurred in connection with the preparation, negotiation, execution and delivery
of this Amendment.
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4.   Continuing Effect of Loan Agreement. Except as expressly amended and modified hereby, the
provisions of the Loan Agreement, and the Liens granted thereunder, are and
shall remain in full force and effect and the waiver set forth herein shall be
limited precisely as drafted and shall not constitute a waiver of any other
provisions of the Loan Agreement.

5.   Counterparts.
This Amendment may be executed in multiple counterparts each of which shall be
deemed to be an original and all of which when taken together shall constitute
one and the same instrument.

6.   Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK APPLICABLE TO
CONTRACTS MADE AND PERFORMED IN SUCH STATE WITHOUT REGARD TO THE PRINCIPLES
THEREOF REGARDING CONFLICTS OF LAWS.

IN WITNESS WHEREOF, the parties hereto
have caused this Amendment to be duly executed and delivered as of the day and
year specified at the beginning hereof.

| | KNOGO NORTH AMERICA INC.,
as Borrower
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   V.P. - CFOSENTRY TECHNOLOGY CORPORATION,
as Credit Party
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   V.P. - CFOVIDEO SENTRY CORPORATION,
as Credit Party
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   V.P. - CFOKNOGO CARIBE, INC.,
as Credit Party
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   TreasurerGENERAL ELECTRIC CORPORATION,
as Lender
By:  /s/ Philip F. Carfora
Name:   Philip F. Carfora
Title:   Duly Authorized Signatory
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CONSENT OF GUARANTORS

Each of the undersigned guarantors does hereby
consent to the execution, delivery and performance of the within and foregoing
Amendment and confirms the continuing effect of such guarantor's guarantee of
the Obligations after giving effect to the foregoing Amendment.

IN WITNESS WHEREOF, each of the
undersigned guarantors has executed this Consent to Guarantors as of the day and
year first above set forth.

| | GUARANTORSSENTRY TECHNOLOGY CORPORATION,
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   V.P. - CFOVIDEO SENTRY CORPORATION,
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   V.P. - CFOKNOGO CARIBE, INC.,
By:  /s/ Peter J. Mundy
Name:   Peter J. Mundy
Title:   Treasurer
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