Document:

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                              AGREEMENT OF SUBLEASE

         THIS AGREEMENT OF SUBLEASE (the "Sublease") is made as of the 5th day
of December, 2000, by and between AMERICAN MANAGEMENT SYSTEMS, INC., a Delaware
corporation (the "Sublessor") having an office at 12701 Fair Lakes Circle,
Fairfax, Virginia, and XYBERNAUT, a Delaware corporation (the "Sublessee")
having an office at 12701 Fair Lakes Circle, Fairfax, Virginia.

                                   WITNESSETH:

         WHEREAS, pursuant to an Office Lease Agreement dated at of August 12,
1993, by and between Landlord and Tenant (the "Original Lease") as amended by
(i) that certain First Amendment to Office Lease Agreement dated August 31, 1994
( the "First Amendment"), (ii) that certain Second Amendment to Office Lease
Agreement dated November 1, 1994 ( the "Second Amendment"), (iii) that certain
'Third Amendment to Office Lease Agreement dated October 2, 1995 (the "Third
Amendment"), (iv) that certain Fourth Amendment to Office Lease Agreement dated
August 12, 1996 (the "Fourth Amendment"), (v) that certain Fifth Amendment to
Office Lease Agreement dated September 30, 1996 ( the "Fifth Amendment"), (vi)
that certain Sixth Amendment to Office Lease Agreement dated August 7, 1998 (the
"Sixth Amendment"), (vii) that certain Seventh Amendment to Office lease
Agreement dated May 3, 1999 (the "Seventh Amendment"), and (viii) that certain
Eighth Amendment to Office Lease Agreement dated October 11, 1999 ( the "Eighth
Amendment") (the Original Lease, First Amendment, Second Amendment, Third
Amendment, Fourth Amendment, Fifth Amendment, Sixth Amendment, Seventh
Amendment, and Eighth Amendment are hereinafter collectively referred to as the
"Lease"), Landlord leased to Tenant certain Premises more particularly described
therein in the building commonly known as Hyatt Plaza, 12701 Fair Lakes Circle,
Fairfax, Virginia 22033 (the "Building"); and

         WHEREAS, Sublessor desires to sublease to Sublessee, and Sublessee
desire to sublease from Sublessor, certain space in the Prime Lease Premises, on
the terms and conditions hereinafter set forth.

         NOW, THEREFORE, in consideration of the mutual covenants herein
contained, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

         1. Subleasing of the Premises. Sublessor hereby subleases to Sublessee
and Sublessee hereby subleases from Sublessor approximately three thousand three
hundred fifty (3,350) rentable square feet of office space on the first (1st)
floor of the Prime Lease premises, as depicted on the plan attached hereto as
Exhibit A, (the "Premises"), upon and subject to all of the terms, covenants,
rentals and conditions hereinafter set forth.

         2. Term. This Sublease shall be in full force and effect from the date
it has been executed by Sublessor and Sublessee and consented to by Landlord.
The term (the "Term") of

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this Sublease shall commence on January 1, 2001, or upon occupancy by Sublessee,
which ever comes first (the "Commencement Date"), and expire on September 30,
2001 (the "Expiration Date"), unless sooner terminated as hereinafter provided.

         3. Rent

              (a) During the Term, Sublessee shall pay to Sublessor, in lawful
money of the United States, the following annual base rent ("Annual Base Rent"),
payable in equal monthly installments (the "Monthly Base Rent"), all as set
forth below. All such Monthly Base Rent is to be paid in advance, with the first
monthly installment to be paid to Sublessor concurrently with Sublessee's
execution of this Sublease and each subsequent monthly installment to be paid to
Sublessor on the first (1st) day of each month during the Term, at the office of
Sublessor, or such other place as Sublessor may designate, without any
abatement, set-off or deduction of any kind whatsoever. If the Commencement Date
is a date other than the first day of a month, rent for the period commencing
with and including the Commencement Date and ending on and including the day
prior to the first day of the following month shall be prorated at the rate on
one-thirtieth (1/30th) of the Monthly Base Rent per day and shall be due and
payable on the Commencement Date.

           Period               Annual Base Rent        Monthly Base Rent

Commencement Date - 9/30/01        $93,800.00                 $7,816.67

           (b) All amounts payable by Sublessee to Sublessor pursuant to this
Sublease shall be deemed and constitute rent and, in the event of any
non-payment thereof and after the lapse of any applicable grace period,
Sublessor shall have all of the rights and remedies provided herein, in the
Lease, and at law or in equity for non-payment of rent. Sublessee's obligation
to pay rent hereunder shall be on account of the period from and after the
Commencement Date and shall survive the Expiration Date or sooner termination of
this Sublease.

           4. Care, Surrender and Restoration of the Premises.

              (a) Without limiting any other provision of this Sublease or the
Lease, Sublessee shall take good care of the premises, suffer no waste or injury
thereto and shall comply with all laws, orders and regulations which are imposed
on Sublessor, as tenant under the Lease, and are applicable to the Premises
and/or Sublessee's use thereof. Upon the Expiration Date or sooner termination
of this Sublease, Sublessee shall quit and surrender the Premises to Sublessor
in the condition such Premises were in on the Commencement Date, broom clean, in
good order and condition, ordinary wear and tear excepted.

              (b) Upon the Expiration Date or sooner termination of this
Sublease, Sublessee shall remove from the Premises at its sole expenses all of
its personal property. Upon removal of Sublessee's property from the Premises,
Sublessee shall, at its sole expense, promptly repair and restore the Premises
to the condition existing prior to the placement of such personal property upon
the Premises and repair any damage to the Premiese and/or the Building related
to such removals, so as to restore the Premises to the condition required under
subsection (a) above.

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All property permitted or required to be removed by Sublessee upon the
Expiration Date or sooner termination of this Sublease remaining on the Premises
after such Expiration Date or sooner termination shall be deemed abandoned and
may, at the election of Sublessor, either be retained as Sublessor's property or
may be removed from the Premises by Sublessor, at Sublessee's expense. Any such
expenses shall be paid by Sublessee to Sublessor upon demand therefor

           5. Use. Sublessee shall use and occupy the Premises, subject to the
terms of the Lease, solely for general office use, and for no other purpose.

           6. Incorporation of Terms of Lease. The terms provisions, covenants,
stipulations, conditions, rights, obligations, remedies and agreements of the
Lease are incorporated into this Sublease by reference and made a part thereof
as if herein set forth at length, and shall, as between Sublessor and Sublessee
(as if they were the Landlord and Tenant, respectively, under the Lease and as
if the Premises being sublet hereby were the Prime Lease Premises demised under
the Lease), constitute the terms of this Sublease, including without limitation,
the late payment fee and interest on past due rent, except to the extent that
they do not expressly relate to the Premises or are expressly inapplicable to,
or expressly modified or eliminated by, the terms of this Sublease (e.g.,
Sublessee shall be obligated to pay the Annual Base Rent and additional rent
described in this Sublease, and not the base rent, escalations thereto and
operating expense and real estate tax pass throughs described in the Lease).
Sublessor and Sublessee each agree to observe and be bound by each and every
covenant, condition and provision of the Lease insofar as any such covenant,
condition or provision affects the Premises or Sublessee's use thereof.
Sublessee acknowledges that it has reviewed and is familiar with the Lease, and
Sublessor represents that the copy of the Lease attached hereto as Exhibit B is
a true, correct and complete copy of the Lease.

           7. Covenants with Respect to the Lease. Except as otherwise expressly
provided herein, all acts to be performed and all of the terms and provisions to
be observed by Sublessor with respect to the Premises, as Tenant under the
Lease, shall be performed and observed by Sublessee. Sublessee covenants and
agrees that Sublessee shall not do anything that would constitute a default
under the Lease or omit to do anything that Sublessee is obligated to do under
the terms of this Sublease so as to cause a default under the Lease.

           8. Utilities and Services.

              (a) Services with be provided to the Premises pursuant to and in
accordance with the terms of Article 7 of the Lease. Utilities will be provided
to the Premises pursuant to and in accordance with the terms of Article 8 of the
Lease.

              (b) Notwithstanding anything to the contrary contained in this
Sublease, Sublessor shall not be obligated to perform for Sublessee any services
of any nature whatsoever or furnish to Sublessee or the Premises any utilities
of any nature whatsoever, including without limitation, heat, electricity, air
conditioning, elevator service, cleaning, window washing or trash removal
services, however, Sublessor shall exercise reasonable efforts to obtain such
utilities and

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services for the Premises from the Landlord pursuant to and in
accordance with the terms of the Lease.

           9. Security Deposit. None

           10. Representations and Warranties; Broker.

              (a) Each party represents and warrants to the other that it has
the power and authority to enter into this Sublease, and that this Sublease is
the valid and binding obligation of such party and is enforceable against it in
accordance with its terms.

              (b) Sublessor and Sublessee represent and warrant to each other
that neither has dealt with any broker in connection with this Sublease.
Sublessor and Sublessee shall indemnify the other against, and hold each other
harmless from any claim of, or liability, to any broker or any party with whom
Sublessor or Sublessee shall have dealt in connection with this transaction or
the Sublease.

           11. Indemnification. Sublessee agrees to indemnify Sublessor and
Landlord (Sublessor and landlord are herein collectively referred to as the
"Indemnified Party") against and hold each Indemnified Party harmless from any
loss, cost, liability or expense (including, without limitation, reasonable
attorneys' fees and related disbursements) insured by such Indemnified Party by
reason of (a) any injuries to persons or damage to property occurring in, on or
about the Premises, other than those arising from the gross negligence or
willful misconduct of such Indemnified Party, (b) any work or thing whatsoever
done or condition created by Sublessee in, on or about the Premises or the
Building, or (c) any act or omission of Sublessee, its agents, contractors,
servants, employees, invitees or licenses, or (d) any failure by Sublessee to
perform or observe any of the covenants and obligations required of Sublessee
under this Sublease, including without limitation, any breach of the Lease
caused or permitted by Sublessee. In addition to, and not in limitation of the
foregoing, wherever the Sublessor as tenant under the Lease has agreed to
indemnify the Landlord, so in this Sublease, Sublessee likewise agrees to
indemnify Sublessor and Landlord. Sublessee's obligations under this Section
shall survive the expiration or termination of this Sublease.

           12. Approvals and Consents. Notwithstanding anything to the contrary
contained in this Sublease, Landlord's consent or approval shall be required for
all matters under this Sublease for which the approval or consent of Landlord is
required under the Lease.

           13. Condition of the Premises; Sublessee's Alterations; Furniture;
Phone/Data Wiring.

              (a) On the Commencement Date, the Premises shall be delivered to
Sublessee in "AS IS" condition substantially consistent with the plan, and notes
to the plan, attached hereto as Exhibit A. Sublessor has the right, but not the
obligation, to require Sublessee, at Sublessee's sole expense, to return any
alteration indicated on Exhibit A to its original condition upon the termination
of this Sublease. Sublessee represents it has made a thorough examination of the
Premises and it is familiar with the condition thereof. Sublessee acknowledges
that it enters into

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this Sublease without any representations or warranties by Sublessor or
Landlord, or anyone acting or purporting to act on behalf of Sublessor or
Landlord, as to the present or future condition of the Premises or the
appurtenances thereto or any improvements therein or of the Building, except as
specifically set forth in this Sublease.

              (b) Notwithstanding anything to the contrary contained in the
Lease, Sublessee shall not make any alterations or changes to the Premises
whatsoever, including, without limitation, structural or non-structural changes,
without the prior written consent of Sublessor and Landlord, pursuant to and in
accordance with the terms and conditions of the Lease.

              (c) Sublessor shall provide Sublessee furniture to be used only
during the term of Sublessee's occupancy of the Premises. In accordance with the
room numbers on Exhibit A, Sublessor will provide conference room furniture for
room number 101 and typical office furniture for room numbers 102, 103, 104,
106, 107, 108, 109, 111, 113 and 115. For its use of the furniture in the
Premises, Sublessee agrees to pay Sublessor, in accordance with the terms and
conditions of Article 3 of this Sublease, nine hundred seventy five dollars
($975.00) on a monthly basis for the duration of this Sublease. Sublessee
represents it has made a thorough examination of the furniture located in the
Premises and it is familiar with the condition thereof. Sublessee acknowledges
that it enters into this Sublease without any representations or warranties by
Sublessor, or anyone acting or purporting to act on behalf of Sublessor, as to
the present or future condition of the furniture located in the Premises, except
as specifically set forth in this Sublease.

              (d) Sublessor shall permit the Sublessee to use all the phone/data
wiring currently located in the Premises for the purposes of Sublessee's
occupancy of the Premises. Sublessee represents it has made a thorough
examination of the phone/data wiring located in the Premises and it is familiar
with the condition thereof. Sublessee acknowledges that it enters into this
Sublease without any representations or warranties by Sublessor, or anyone
acting or purporting to act on behalf of Sublessor, as to the present or future
condition of the phone/data wiring located in the Premises, except as
specifically set forth in this Sublease.

           14. Time Limits. In the event Sublessee receives from Sublessor any
notice to cure any default hereunder or under the Lease which notice is based on
a notice sent to Sublessor by Landlord pursuant to the Lease, Sublessee shall
cure such condition three (3) days prior to the time required of Sublessor by
Landlord for the cure thereof.

           15. Assignment and Subletting. Sublessee, for itself, its successors
and assigns, expressly covenants that it shall not assign, whether by operation
of law or otherwise, or pledge or otherwise encumber this Sublease, or sublet
all or any part of the Premises. Any such attempted assignment or subletting
shall be void and of no force and effect. Sublessor reserves the right to
transfer and assign its interest in and to this Sublease to any entity or person
whom shall succeed to Sublessor's interest in and to the Lease.

           16. Insurance.

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              (a) Sublessee shall obtain and keep in full force and effect
during the Term with regard to the Premises, at its sole cost and expense,
commercial general public liability insurance, property damage insurance, and
fire and extended coverage insurance and any other insurance coverage required
to be obtained by Sublessor, as tenant under the Lease, and such insurance
coverage shall be in the nature and amounts set forth therein. Such insurance
policies shall name Sublessor and Landlord (and such other person as Sublessor
may request by notice to Sublessee from time to time) as additional insureds
thereunder. Any reference to Landlord in that provisions of the Lease relating
to the tenant's insurance requirements shall include both Sublessor and
Landlord. Sublessee shall pay all premiums and charges for such insurance. If
Sublessee shall fail to obtain such insurance, Sublessor may, but shall not be
obligated to, obtain the same, in which event the amount of the premium paid
shall be paid by Sublessee to Sublessor upon Sublessor's demand therefor. Such
amount shall be deemed additional rent hereunder and shall be collectible by
Sublessor in the same manner and with the same remedies as though said sums were
Monthly Base Rent reserved hereunder.

              (b) On or before the date of this Sublease, Sublessee shall
furnish to Sublessor and Landlord certificates evidencing the aforesaid
insurance coverage, and renewal certificates shall be furnished to Sublessor and
Landlord at least thirty (30) days prior to the expiration of each policy for
which a certificate was theretofore furnished. All insurance policies required
of Sublessee hereunder shall provide that Sublessor and Landlord will be given
at least thirty (30) days prior written notice of any cancellation or material
change in the policy, or any other expiration or defaults thereunder.

              (c) Sublessee acknowledges that neither Landlord nor Sublessor
will carry any insurance in favor of Sublessee, of Sublessee's furniture,
fixtures, equipment, improvements, appurtenances or other property of Sublessee
in or about the Premises.

           17. Release and Waiver of Subrogation. Any property damage, fire or
extended coverage insurance policy obtained by Sublessee, and covering the
Premises or the personal property, fixtures and equipment located therein or
thereon, shall contain an endorsement pursuant to which the respective insurance
companies waive subrogation against Landlord and Sublessor. Sublessee hereby
releases Sublessor and Landlord to the limits of the coverage of the insurance
policies required to be held by Sublessee under this Sublease with respect to
any claim (including a claim for negligence) which it might otherwise have
against Sublessor and Landlord for loss, damage or destruction with respect to
its property.

           18. Hold-Over. If Sublessee shall not immediately surrender the
Premises at the end of the Term, then Sublessee shall, by virtue of this
Sublease, become a tenant at sufferance at a monthly rental equal to twice the
Monthly Base Rent plus any additional rent due under the terms of this Sublease,
commencing with the first day following the end of the Term. Sublessee, as a
tenant at sufferance, shall be subject to all of the conditions and covenants of
this Sublease (including payment of additional rent) as though the tenancy had
originally been a monthly tenancy. During the holdover period, each party hereto
shall give to the other at least thirty (30) days written notice to quit the
Premises, except in the event of nonpayment of Monthly Base Rent or additional
rent when due, or of the breach of any other provision hereof by sublessee, in

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which event, Sublessee shall not be entitled to any notice to
quit, the usual thirty (30) days notice to quit being expressly waived.

           19. Extension of Term. Provided that Sublessee has not been in an
event of default during the term of the Sublease, Sublessee may be granted two
(2) renewal terms of six (6) months each provided all the following terms are
satisfied:

              (a) Under no circumstance will the Sublessee be permitted to
extend this Sublease providing an Expiration Date that is later than the
Expiration Date for the Premises provided in the Lease.

              (b) As for the first extension term, Sublessee must provide a
written request to renew no later than May 1, 2001. Sublessor has the express
right to approve or reject Sublessee's request for a renewal. Sublessor will
either approve or reject Sublessee's request forrenewal, in writing, no later
than June 1, 2001. If Sublessor does not provide written approval or rejection
of the Sublessee's request for renewal by June 1, 2001, then Sublessee's request
is deemed to be rejected. Should Sublessee's request for renewal be rejected,
then Sublessee will surrender the Premises in accordance with Article 4 of this
Sublease.

              (c) The second extension term can only be requested by the
Sublessee in the case that the first extension term was approved in writing by
the Sublessor. As for the second extension tern, Sublessee must provide a
written request to renew no later then November 1, 2001. Sublessor has the
express right to approve or reject Sublessee's request for a second renewal.
Sublessor will either approve or reject Sublessee's request for a second
renewal, in writing, no later than January 1, 2002. If Sublessor does not
provide written approval or rejection of the Sublessee's request for a second
renewal by January 1, 2002, then Sublessee's request is deemed to be rejected.
Should Sublessee's request for a second renewal be rejected, then Sublessee will
surrender the Premises in accordance with Article 4 of this Sublease.

           20. Notices.

              (a) Any notice, demand or communication required or desired
hereunder by either party to the other shall be in writing and shall be given
when personally delivered or three (3) days after sent by certified or
registered mail, first class, postage prepaid, or one (1) business day after
delivery to a recognized national overnight courier, to the party for whom
intended (i) prior to the Commencement Date, at the respective addresses of
Sublessor and Sublessee first set forth above, and (ii) from and after the
Commencement Date, at the Building when sent to Sublessee. Either party may, by
like written notice, designate a new address to which such notice, demand, or
communication shall thereafter be given.

              (b) Sublessee shall promptly after receipt thereof, furnish to
Sublessor by hand delivery a copy of any notice, demand or other communication
received from Landlord with respect to the Premises.

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           21. Landlord's Consent.

              (a) Sublessor and Sublessee each acknowledge and agree (i) that
this Sublease is subject to, and will not be effective without the receipt of,
the written consent of Landlord in accordance with the terms of the Lease, and
(ii) that Landlord's consent to this Sublease shall not create any contractual
liability or duty on the part of Landlord to Sublessee, and shall not in any
manner increase, decrease or otherwise affect the rights and obligations of
Landlord and Sublessor, as landlord and tenant under the Lease, with respect to
the Premises.

              (b) This Sublease is subject and subordinate to the Lease and to
the matters to which the Lease is or shall be subordinate. In the event of the
termination of the Lease, or the re-entry or dispossession of Sublessor, as
tenant, by Landlord under the Lease, Landlord, at its option, may either
terminate this Sublease, in which case Sublessee shall peacefully vacate the
Premises, or require Sublessee to attorn to Landlord as its sublessor pursuant
to the then applicable terms of this Sublease for the remaining term hereof,
except that Landlord shall not be (i) liable for damages for any previous act or
omission of Sublessor under this Sublease, (ii) subject to any offset which
theretofore accrued to Sublessee against Sublessor, or (iii) bound by any
previous modification of this Sublease not consented to in writing by Landlord
or by a previous prepayment of rent more than one month in advance.

           22. Miscellaneous.

              (a) This Sublease may not be extended, renewed, terminated (other
than in accordance with the terms hereof), or otherwise modified except by an
instrument in writing signed by the party against whom enforcement of any such
modification is sought.

              (b) It is understood and agreed that all understandings and
agreements heretofore had between the parties hereto are merged in this
Sublease, which alone fully and completely expresses their agreement. This
Sublease has been entered into after full investigation, neither party relying
upon any statement, representation or warranty made by the other not embodied in
this Sublease.

              (c) The section headings appearing herein are for purposes of
convenience only and are not deemed to be a part of this Sublease.

              (d) The provisions of this Sublease shall be governed by and
construed in accordance with the laws of the Commonwealth of Virginia.

              (e) Time is of the essence as to the obligations contained in this
Sublease.

              (f) Sublessor and Sublessee each hereby waive trial by jury in any
action, proceeding or counterclaim brought by either of them against the other
in connection with any matter arising out of or in any way connected with this
Sublease, Sublessee's use or occupancy of the Premises, and/or any claim for
injury or damages.

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              (g) Sublessor and Sublessee each hereby agree that neither shall
be permitted to record this Sublease nor any memorandum nor assignment thereof.

                             SIGNATURE PAGE FOLLOWS

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         IN WITNESS WHEREOF, this Sublease has been duly executed as of the day
and year first above written.

WITNESS/ATTEST:                         SUBLESSOR:

-----------------------------           AMERICAN MANAGEMENT SYSTEMS, INC.

                                        By:
                                            ------------------------------------
                                        Name:
                                            ------------------------------------
                                        Its:
                                            ------------------------------------

WITNESS/ATTEST:                         SUBLESSEE:

-----------------------------           XYBERNAUT CORPORATION

                                        By:
                                          --------------------------------------
                                        Name:
                                          --------------------------------------
                                        Its:
                                          --------------------------------------

                                      -10-
<PAGE>   11
                                    EXHIBIT A

                                PLAN OF PREMISES

                                      -11-<PAGE>   1
                                                                     EXHIBIT 4.1

                           CONVERTIBLE PROMISSORY NOTE

$142,526.00                                                    February 27, 2001

         For value received, INTEGRATED SECURITY SYSTEMS, INC., a Delaware
corporation (hereinafter referred to as "Maker"), promises to pay to the order
to HBW CAPITAL FUND, L.P. (hereinafter referred to as "Payee"), the principal
sum of One Hundred Forty Two Thousand Five Hundred Twenty Six and No/100 Dollars
($142,526.00). The principal of and interest on this Note shall be due and
payable in lawful money of the United States of America, at the office of Payee
at 13355 Noel Road, Suite 1650, Dallas, Texas 75240, or at such other place as
the holder hereof may from time to time designate by written notice to Maker.

         1.       Interest. Interest shall accrue on the unpaid principal
balance under this Note at an annual rate equal to nine percent (9%). Interest
shall accrue from and including the date of this Note until, but not including,
the day on which it is paid in full. In no event shall the interest charged
hereunder exceed the maximum rate of interest allowed from time to time by law.
Interest shall be due and payable monthly on the first (1st) day of each month.

         2.       Payment of Note. The principal balance of, and all accrued
unpaid interest on, this Note shall be due and payable one hundred twenty (120)
days from the date hereof, except as otherwise provided herein. ("Maturity
Date").

         3.       Prepayment. This Note may be prepaid in whole or in part at
any time, at the option of Maker, without premium or penalty.

         4.       Conversion. This note shall be convertible, at the option of
Payee in its sole and absolute discretion, in whole or in part and at any time
or from time to time, into fully paid and nonassessable shares (the "Conversion
Shares") of Common Stock, $.01 par value (the "Common Stock"), of Integrated
Security Systems, Inc., a Delaware corporation (the "Company"), at the
conversion price of $0.20 per share. If Payee elects to exercise its option, the
the following shall occur:

                  (a) Payee shall deliver to Maker a notice of such election
                  (the "Conversion Notice"), indicating the amount of principal
                  of this Note to be converted (such amount to be converted
                  referred to herein as the "Converted Amount").

                  (b) Promptly upon receipt of the Conversion Notice, Maker
                  shall deliver to the Company (i) a certificate or certificates
                  of Maker's Common Stock representing at least the number of
                  shares issuable to Payee upon conversion of the Converted
                  Amount, duly endorsed in blank or accompanied by a stock
                  transfer power executed in like manner, and (ii) a copy of the
                  Conversion Notice.

                                       1
<PAGE>   2

                  (c) Upon its receipt of Maker's endorsed Common Stock
                  certificate(s) and the Conversion Notice, the Company shall
                  immediately issue and deliver to Payee or its designated
                  affiliates a certificate or certificates for the number of
                  shares of Common Stock, registered in Payee's or its
                  designated affiliates' name(s), to which Payee shall be
                  entitled upon such conversion, bearing such legends as may be
                  required by applicable state and federal securities laws. The
                  Company shall issue to Maker a certificate representing any
                  shares surrendered by Maker in excess of the shares issued to
                  Payee upon conversion.

                  (d) If this Note is converted in whole, Payee shall deliver
                  this Note to Maker marked "Cancelled," and Maker shall
                  immediately pay to Payee all accrued and unpaid interest then
                  due and owing on the date of such conversion. If this Note is
                  converted in part, Maker shall immediately pay to Payee all
                  accrued and unpaid interest then due and owing on the date of
                  such conversion, and Payee shall deliver to Maker a
                  replacement Note for any outstanding principal amount not
                  converted. Dated the date of such conversion, with the same
                  Maturity Date and provisions as contained in this Note.

                  (e) No fractional shares will be issued on conversion of this
                  Note.

         5.       Adjustment for Issuance of Shares at Less Than the Conversion
Price. If and whenever any Additional Common Stock (herein defined) shall be
issued by Maker (the "Stock Issue Date") for a consideration per share less than
the Conversion Price, Then in each such case the initial Conversion Price shall
be reduced to a new Conversion Price in an amount equal to the price per share
of the Additional Common Stock the issued, as determined in accordance with
general accepted accounting principles, if issued other than for cash, and the
number of shares issuable to Payee upon conversion shall be proportionately
increased; and, in the case of Additional Common Stock issued without
consideration, the initial Conversion Price shall be reduced in amount and the
number of shares issued upon conversion shall be increased in an amount so as to
maintain for the Payee the right to convert this Note into shares equal in
amount to the same percentage interest in the Common Stock of the Company as
existed for the Payee immediately preceding the Stock Issue Date.

         6.       Sale of Shares. In case of the issuance of Additional Common
Stock for a consideration part or all of which shall be cashed, the amount of
the cash consideration therefore shall be deemed to be the gross amount of the
cash paid to Maker for such shares, before deducting any underwriting
compensation or discount in the sale, underwriting or purchase thereof by
underwriters or dealers or others performing similar services for any expenses
incurred in connection therewith. In case of the issuance of any shares of
Additional Common Stock for a consideration part or all of which shall be other
than cash, the amount of the consideration therefore, other than cash, shall be
deemed to be the then fair market value of the property received.

                                       2
<PAGE>   3

         7.       Stock Dividends. Shares of Common Stock issued as a dividend
or other distribution on any class of capital stock of Maker shall be deemed to
have been issued without consideration.

         8.       Stock Splits, Subdivisions or Combinations. In the event of a
stock split or subdivision of shares of Common Stock into a greater number of
shares, the Conversion Price shall be proportionately decreased, and in the
event of a combination of shares of Common Stock into a smaller number of
shares, the Conversion Price shall be proportionately increased, such increase
or decrease, as the case may be, becoming effective at the record date.

         9.       Exceptions. The term "Additional Common Stock" herein shall
mean all shares of Common Stock hereafter issued by Maker (including Common
Stock held in the treasury of Maker), except for (A) Common Stock issued upon
the conversion of this Note; (B) Common Stock issued upon exercise of any
outstanding warrants, options or convertible debt instruments; and (C) Common
Stock issued upon exercise of outstanding employee stock options.

         10.      Adjustment for Mergers, Sales and Consolidations. In the event
of any consolidation or merger of the Company with or into, or the sale of all
or substantially all of the properties and assets of the Company, to any person,
and in connection therewith, consideration is payable to holders of Common Stock
in cash, securities or other property, then as a condition of such
consolidation, merger or sale, lawful provision shall be made, and duly executed
documents evidencing the same shall be delivered to the Payee, so that the Payee
shall have the right at any time prior to the maturity of this Note to purchase,
at a total price equal to the Conversion Price immediately prior to such event,
the kind and amount of cash , securities or other property receivable in
connection with such consolidation, merger or sale, by a holder of the same
number of shares of Common Stock as were exercisable by the Payee immediately
prior to such consolidation, merger or sale. In any such case, appropriate
provision shall be made with respect to the rights and interest of the Payee so
that the provisions hereof shall thereafter be applicable with respect to any
cash, securities or property deliverable upon exercise hereof. Notwithstanding
the foregoing, (i) if the Company merges or consolidates with or sells all or
substantially all of its property and assets to, any other person, and
consideration is payable to holders of Common Stock in exchange for their Common
Stock in connection with such merger, consolidation or sale which consists
solely of cash, or (ii) in the event of the dissolution, liquidation or winding
up of the Company, then the Payee shall be entitled to receive distributions on
the date of such event on an equal basis with holders of Common Stock as if this
Note had been converted immediately prior to such event, less the Conversion
Price. Upon receipt of such payment, if any, the rights of the Payee shall
terminate and cease and this Note shall expire. In case of any such merger,
consolidation or sale of assets, the surviving or acquiring person and, in the
event of any dissolution, liquidation or wind up of the Company, the Company
shall promptly, after receipt of this surrendered Note, make payment by
delivering a check in such amount as is appropriate (or, in the case of
consideration other than cash, such other consideration as is appropriate) to
such person as it may be directed in writing by the Payee surrendering this
Note.

                                       3
<PAGE>   4

         11.      Adequate Shares. Maker will at times reserve and keep
available, for the purpose of issuance upon conversion, a sufficient number of
shares of Common Stock owned by Maker deliverable upon Payee's exercise of its
conversion rights under this Note.

         12.      Default, Enforcement. Upon default in payment of this Note,
Payee may pursue any and all remedies to which Payee may be entitled.

         13.      Limitation of Interest. All agreements between Maker and
Payee, whether now existing or hereafter arising and whether written or oral,
are expressly limited so that in no contingency or event whatsoever, whether by
reason of advancement of the proceeds hereof, acceleration or the maturity of
the unpaid principal balance hereof, or otherwise, shall the amount contracted
for, charged, received, paid or agreed to be paid to the holder hereof for the
use, forbearance or detention of the money evidenced by this Note or for the
payment or performance of any covenant or obligation contained herein or in any
other document pertaining to the indebtedness evidenced by this Note exceed the
maximum amount permissible under applicable usury laws. If, from any
circumstance whatsoever, fulfillment of any provision hereof or of any other
agreement shall, at the time fulfillment of such provision be due, involve
transcending the limits of validity prescribed by law which a court of competent
jurisdiction may deem applicable hereto the ipso facto, the obligation to be
fulfilled shall be reduced to the limit of such validity; and if from any
circumstance the holder hereof shall ever receive as interest an amount which
would exceed the maximum lawful rate, any amount equal to any excessive interest
shall (a) be applied to the reduction of the unpaid principal balance due
hereunder and not to the payment of interest, or (b) if such excess interest
exceeds the unpaid principal balance of this Note, such excess shall be refunded
to Maker. All sums contracted for, charged or received hereunder for the use,
forbearance or detention of the indebtedness evidenced hereby shall, to the
extent permitted by applicable law, be amortized, prorated, allocated and spread
throughout the full term of this Note until payment in full so that the rate of
interest on account of such indebtedness is uniform throughout the term hereof.
The terms and provisions of this paragraph shall control and supersede every
other provision of all agreements between Maker and the holder hereof.

         14.      Waiver. Except as otherwise expressly provided herein, Maker
waives demand, notice of intent to accelerate, notice of acceleration, notice of
nonpayment or dishonor, grace, protest, notice of protest, all other notices,
and any and all diligence or delay in collection or the filing of suit hereon.

         15.      Governing Law and Venue. This Note shall be construed
according to and governed by the laws of the State of Texas. The obligations of
Maker under this Note are performable in Dallas County, Texas.

         16.      Registration Rights. The shares of Common Stock issued upon
conversion of this Note shall be restricted from transfer by the Payee, unless
the shares are duly registered for sale pursuant to the Securities Act of 1933,
as amended, or the transfer is exempt from registration.

                                       4
<PAGE>   5

         17.      Security Agreement. This Note is secured by the accounts
receivable of Intelli-Site, Inc.

         18.      Successors and Assigns. This Note shall bind Maker's
successors and assigns.

         19.      Collection Costs. If this Note is collected by legal
proceeding or through a probate or bankruptcy court, or is placed in the hands
of an attorney for collection after default (whether or not suit is filed),
Maker agrees to pay all costs of collection and/or suit, including but not
limited to reasonable attorney's fees incurred by Payee.

         20.      Unenforceability. The invalidity or unenforceability in
particular circumstances of any provision of this Note shall not extend beyond
such provision or such circumstances, and no other provision of this Note shall
be affected thereby.

         21.      Headings. The paragraph headings of the sections of this Note
are inserted for convenience of reference only and shall not affect the meaning
or interpretation of this Note.

         IN WITNESS WHEREOF, Maker has duly executed this Note as of the day and
year first above written.

                                      INTEGRATED SECURITY SYSTEMS, INC.

                                      BY: /s/ C.A. Rundell, Jr.
                                         ------------------------------------
                                         C. A. Rundell, Jr.
                                         Chairman and Chief Executive Officer

                                       5

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