Document:

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                                                                    EXHIBIT 4.12
                                    [FORM OF]
                                 PROMISSORY NOTE

[Dollar Amount]                                                           [Date]

         For value received, INTEGRATED SECURITY SYSTEMS, INC., a Delaware
corporation (hereinafter referred to as "Maker"), promises to pay to the order
of __________________, [an individual] [a _____________ corporation]
(hereinafter referred to as "Payee"), the principal sum of _________________ and
[no/100] Dollars ($_______________). The principal of and interest on this Note
shall be due and payable in lawful money of the United States of America, at the
offices of Payee at ____________________________________, 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 due
under this Note at an annual rate equal to ______ percent (__%). 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 on interest allowed from time to time by law.

         2. Payment of Note. The principal balance of and all accrued unpaid
interest on this Note shall be due and payable on demand.

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

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

         5. 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

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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.

         6. Waiver. Except as otherwise expressly provided herein, Maker waives
demand, presentment for payment, 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.

         7. 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.

         8. Security Agreement This Note is secured by the Security Agreement
among Maker, B&B Electromatic, Inc., Golston Company, Inc., Innovative Security
Technologies, Inc. (now named Intelli-Site, Inc.) and Tri-Coastal Systems, Inc.
and Payee and Renaissance US Growth and Income Trust PLC ("RUSGIT"), dated as of
October 2, 1998, and Payee is entitled to the rights and benefits
thereunder.

         9. Stock Pledge Agreement. This Note is secured by the Stock Pledge
Agreement dated as of December 31, 1996, as amended by the First Amendment to
Stock Pledge Agreement, dated May 5, 2000, among Maker, Payee and RUSGIT, and
Payee is entitled to the rights and benefits thereunder.

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

         11. 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.

         12. 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.

         13. 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:
                                                  ------------------------------
                                                  [Name]
                                                  President and CEO
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                            Schedule to Exhibit 4.12

         This Schedule to the form of promissory note shows the date, payee, and
amount of promissory note issued by the Company that are in the format of this
form of promissory note. Each of these notes accrues interest at a rate of 9%
per year.

<TABLE>
<CAPTION>
Date                                      Payee                                   Amount of Loan ($)
----                                      -----                                   -----------------
<S>                     <C>                                                       <C>
August 12, 1999       Renaissance Capital Growth & Income Fund III, Inc.             $115,000
August 12, 1999       Renaissance US Growth & Income Trust PLC                        115,000
May 5, 2000           Renaissance Capital Growth & Income Fund III, Inc.              150,000
May 5, 2000           Renaissance US Growth & Income Trust PLC                        150,000
August 25, 2000       Renaissance Capital Growth & Income Fund III, Inc.              100,000
August 25, 2000       Renaissance US Growth & Income Trust PLC                        100,000
September 15, 2000    Renaissance Capital Growth & Income Fund III, Inc.              100,000
September 15, 2000    Renaissance US Growth & Income Trust PLC                        100,000
September 29, 2000    Renaissance Capital Growth & Income Fund III, Inc.               50,000
September 29, 2000    Renaissance US Growth & Income Trust PLC                         50,000
</TABLE><PAGE>   1
                                                                    EXHIBIT 4.13

                               SECURITY AGREEMENT

         THIS SECURITY AGREEMENT ("Agreement"), dated as of March 8, 1999,
between INTEGRATED SECURITY SYSTEMS, INC., a Delaware corporation, B&B
ELECTROMATIC, INC., a Delaware corporation, GOLSTON COMPANY, INC., a Texas
corporation, INNOVATIVE SECURITY TECHNOLOGIES, INC., a Texas corporation, and
TRI-COASTAL SYSTEMS, INC., a Delaware corporation (collectively, "Debtor"), and
THE RUNDELL FOUNDATION ("Secured Party"). Capitalized terms used herein, unless
otherwise defined herein, have the definitions given them in the Notes (as
defined below).

         WHEREAS, Debtor has issued to Secured Party a promissory note of even
date herewith (the "Notes"), in the aggregate principal amount of $200,000 (the
"Loan");

         WHEREAS, as a condition for providing the Loan, Secured Party required
that Debtor grant a security interest in its assets as collateral for such Loan;

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements set forth herein, the parties hereto and hereby agree
as follows:

         1. Grant of Security Interest. In order to secure payment when due of
all obligations arising under the Notes and all other indebtedness of Debtor to
Secured Party, whether pursuant to subsequently-issued notes or otherwise, now
existing or hereafter incurred (the "Obligations"), Debtor hereby irrevocably
grants to Secured Party a continuing security interest in the following property
of Debtor, whether now owned or existing, or hereafter acquired, owned, existing
or arising (whether by contract or operation by law), and wherever located (the
"Collateral"), which shall be retained by Secured Party until the Obligations
have been paid in full and the Notes has been terminated:

            a. All accounts, contract rights, chattel paper and rights of
payment of every kind (collectively, "Accounts") and instruments and general
intangibles of Debtor.

            b. All bank accounts of Debtor.

            c. All monies, residues and property of any kind, now or at any time
or times hereafter, in the possession or under the control of Secured Party or a
bailee of Secured Party.

            d. All licenses, patents, patent applications, copyrights,
trademarks, trademark applications, trade names, assumed names, service marks
and service mark applications of Debtor.

            e. All inventory, equipment (including any and all computer hardware
and components), machinery and fixtures of Debtor in all forms and wherever
located, and all parts and products thereof, all accessories thereto, and all
documents therefor.

            f. All books and records (including, without limitation, customer
lists, credit files, tapes, ledger cards, computer software and hardware,
electronic data processing software,

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computer programs, printouts and other computer materials and records) of Debtor
evidencing or containing information regarding or otherwise pertaining to any of
the foregoing.

            g. All accessories to, substitutions for and all replacements,
products and proceeds of the foregoing, including, without limitation, proceeds
of insurance policies insuring the Collateral (including, but not limited to,
claims paid and premium refunds).

         2. Insurance on Collateral. Debtor further warrants and agrees that in
each case where the terms of any such Accounts require Debtor or the account
debtor named in such Account to place or carry insurance in respect of the
property to which such Account relates, Debtor or the account debtor will pay
for and maintain such insurance.

         3. Delivery of Receivables. Upon Secured Party's request, upon the
occurrence of an Event of Default, Debtor will, at any reasonable time and at
Debtor's own expense, physically deliver to Secured Party all Accounts assigned
to Secured Party at any reasonable place or places designated by Secured Party.
Failure to deliver any Account, or failure to deliver physical possession of any
instruments, documents or writings in respect of any Account shall not
invalidate Secured Party's Lien and security interest therein, except to the
extent that possession may be required by applicable law for the perfection of
said Lien or security interest, in which latter case, the Account shall be
deemed to be held by Debtor as the custodian agent of Secured Party, for the
benefit of Secured Party. Failure of Secured Party to demand or require Debtor
to include any Account in any schedule, to execute any schedule, to assign and
deliver any schedule or to deliver physical possession of any instruments,
documents or writings related to any Account shall not relieve Debtor of its
duty so to do.

         4. Collection of Receivables. Debtor hereby agrees that it shall use
commercially reasonable efforts, at its sole cost and expense and in its own
name, to promptly and diligently collect and enforce payment of all Accounts and
Debtor will defend and hold Secured Party harmless from any and all loss,
damage, penalty, fine or expense arising from such collection or enforcement.

         5. Financing Statements. Debtor agrees to execute all financing
statements and amendments thereto as Secured Party may request from time to time
to evidence the security interest granted to Secured Party hereunder and will
pay all filing fees and taxes, if any, necessary to effect the filing thereof.
Wherever permitted by law, Debtor authorizes Secured Party to file financing
statements with respect to the Collateral without the signature of Debtor.
Without the written consent of Secured Party, Debtor will not allow any
financing statement or notice of assignment to be on file in any public office
covering any Collateral, proceeds thereof or other matters subject to the
security interest granted to Secured Party herein, unless such financing
statement relates to a Permitted Lien.

         6. Secured Party's Payment of Claims. Secured Party may, in its sole
discretion, discharge or obtain the release of any security interest, lien,
claim or encumbrance asserted by any Person against the Collateral, other than a
Permitted Lien. All sums paid by Secured Party in respect thereof shall be
payable, on demand, by Debtor to such Secured Party and shall be a part of the
Obligations.

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         7. Default and Remedies.

            a. Debtor shall be in default hereunder upon the occurrence of an
Event of Default, as set forth in the Notes.

            b. Upon the occurrence of any Event of Default which shall be
continuing, (i) unless Secured Party shall elect otherwise, the entire unpaid
amount of due under the Continuing Guaranty as are not then otherwise due and
payable shall become immediately due and payable without notice to Debtor or
demand by Secured Party and (ii) Secured Party may, at its option, exercise from
time to time any and all rights and remedies available to them under the Uniform
Commercial Code or otherwise, including the right to foreclose or otherwise
realize upon the Collateral and to dispose of any of the Collateral at one or
more public or private sales or other proceedings, and Debtor agrees that
Secured Party or its nominee may become the purchaser at any such sale or sales.
Debtor agrees that ten (10) days shall be reasonable prior notice of the date of
any public sale or other disposition of the same may be made. All rights and
remedies granted Secured Party hereunder or under any other agreement between
Secured Party and Debtor shall be deemed concurrent and cumulative and not
alternative, and Secured Party may proceed with any number of remedies at the
same time or at different times until all the Obligations are fully satisfied.
The exercise of any one right or remedy shall not be deemed a waiver or release
of or an election against any other right or remedy. Debtor shall pay to Secured
Party on demand any and all expenses (including reasonable attorneys' fees and
legal expenses) which may have been incurred by Secured Party (i) in the
prosecution or defense of any action growing out of or connected with the
subject matter of this Agreement, the Continuing Guaranty, the Collateral or any
of Secured Party's rights therein or thereto; or (ii) in connection with the
custody, preservation, use, operation, preparation for sale or sale of the
Collateral, the incurring of all of which are hereby authorized to the extent
Secured Party deems the same advisable. Debtor's liability to Secured Party for
any such payment shall be included in the Obligations. The proceeds of any
Collateral received by Secured Party at any time before or after default,
whether from a sale or other disposition of Collateral or otherwise, or the
Collateral itself, may be applied to the payment in full or in part of such of
the Obligations and in such order and manner as Secured Party may elect.

         8. Representations and Covenants of Debtor. Debtor hereby represents to
and agrees with Secured Party as follows:

            a. Debtor owns the Collateral as sole owner, free and clear of any
Liens, except as set forth on SCHEDULE A hereto.

            b. So long as any amounts due pursuant to the Notes remain unpaid,
Debtor agrees not to sell, assign or transfer the Collateral and to maintain it
free and clear of any Liens.

         9. Miscellaneous.

            a. This Agreement shall bind and inure to the benefit of the parties
and their respective heirs, personal representatives, successors and assigns,
except that Debtor shall not assign any of its rights hereunder without Secured
Party's prior written consent.

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            b. Any provision hereof which is prohibited or unenforceable in any
jurisdiction shall, as to such jurisdiction, be ineffective to the extent of
such prohibition or unenforceability without affecting the validity or
enforceability of the remainder of this Agreement or the validity or
enforceability of such provision in any other jurisdiction.

            c. All issues arising hereunder shall be governed by the laws of the
State of Texas.

            d. Debtor hereby consents to the jurisdiction of the courts of the
State of Texas in any action or proceeding which may be brought against it under
or in connection with this Agreement or any transaction contemplated hereby or
to enforce any agreement contained herein, and in the event any such action or
proceeding shall be brought against it, Debtor agrees not to raise any objection
to such jurisdiction or to the laying of venue in Dallas County, Texas or, if
applicable, any other county in any state in which Collateral is located.

                                       4
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         IN WITNESS WHEREOF, this Agreement has been duly executed as of the
date and year written above.

                                       DEBTOR:

                                       INTEGRATED SECURITY SYSTEMS, INC.

                                       By:
                                           -------------------------------------
                                           Gerald K. Beckmann
                                           President and Chief Executive Officer

                                       B&B ELECTROMATIC, INC.

                                       By:
                                           -------------------------------------

                                       GOLSTON COMPANY, INC.

                                       By:
                                           -------------------------------------

                                       INNOVATIVE SECURITY TECHNOLOGIES, INC.

                                       By:
                                           -------------------------------------

                                       TRI-COASTAL SYSTEMS, INC.

                                       By:
                                           -------------------------------------

                                       5
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                                       SECURED PARTY:

                                       THE RUNDELL FOUNDATION

                                       By:
                                           -------------------------------------

                                       6
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                                   SCHEDULE A

                               LIENS ON COLLATERAL

         1. Lien in favor of USL Corporation

         2. Lien in favor of Frost National Bank

         3. Lien in favor of Renaissance Capital Growth & Income Fund III, Inc.

         4. Lien in favor of Renaissance US Growth & Income Trust PLC

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