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                                                                     EXHIBIT 4.2

                           CONVERTIBLE PROMISSORY NOTE

$150,000.00                                                      April 11, 2001

         For value received, INTEGRATED SECURITY SYSTEMS, INC., a Delaware
corporation (hereinafter referred to as "Maker"), promises to pay to the order
of FROST NATIONAL BANK FBO RENAISSANCE US GROWTH & INCOME TRUST PLC, a Texas
corporation (hereinafter referred to as "Payee"), the principal sum of One
Hundred Fifty Thousand Dollars ($150,000.00). The principal of and interest on
this Note shall be due and payable in lawful money of the United States of
America, c/o Security Processing T-8, P. O. Box 2479, San Antonio, Texas 78298.
All correspondence and notices should be mailed to the above address with a copy
to the offices of Payee at 8080 N. Central Expressway, Suite 210, Dallas, Texas
75206, 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 eight percent (8%). 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.
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
after the date hereof, except as otherwise provided herein ("Maturity Date").

         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. 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, then 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.

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                           (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 "Canceled," 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 then issued, if issued in connection with a sale of
shares, or the value of the Additional Common Stock then 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 cash, the amount of the cash
consideration therefor 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 therefor, other than cash, shall be deemed to be the
then fair market value of the property received.

         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.

         10. 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

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shares, the Conversion Price shall be proportionately increased, such increase
or decrease, as the case may be, becoming effective at the record date.

         11. 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
provisions 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 winding 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.

         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

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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 limit of validity prescribed by law which a court of competent
jurisdiction may deem applicable hereto, then, 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, 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.

         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. The Payee has certain
rights with respect to the registration of shares of Common Stock issued upon
the conversion of this note pursuant to the terms of the Registration Rights
Agreement between Payee and maker dated October 20, 2000.

         17. 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 fund III, Inc., dated as of
October 2, 1998, and Payee is entitled to the rights and benefits thereunder.

         18. 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 Renaissance
Capital Growth & Income Fund III, Inc., and Payee is entitled to the rights and
benefits thereunder.

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

         20. 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.

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         21. 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.

         22. 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.
                                          President and CEO

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                                                                 EXHIBIT 10.1

                              CALAVO GROWERS, INC.

                              MARKETING AGREEMENT

GROWER'S NAME ____________________________________________________
GROWER'S ADDRESS _________________________________________________
GROWER'S TAXPAYER I.D. NUMBER ____________________________________
GROWER'S ELECTION: ____ MONTHLY OR ____ WEEKLY POOL
EFFECTIVE DATE OF AGREEMENT ______________________________________
GROVE LOCATION ___________________________________________________
NUMBER OF TREES ____________

     This Marketing Agreement (the "Agreement") is entered into by and between
the above-named grower (the "Grower") and Calavo Growers, Inc. ("Calavo"), a
California corporation whose address is 2530 Red Hill Avenue, Santa Ana,
California 92705-5542. The effective date of this Agreement is specified above.
However, if this Agreement is being executed by the parties prior to the merger
of Calavo Growers of California, a California nonprofit cooperative association,
into Calavo, the effective date of this Agreement will be the date on which the
merger occurs. Calavo will advise the Grower of the date of the merger, and
neither party will have any obligations under this Agreement until the merger
occurs.

     The Grower represents that it is the producer of California avocados.
Calavo desires to pack and market these avocados. The following terms are hereby
agreed upon by both parties:

1. Delivery

     The Grower will deliver to Calavo all of the avocados grown by the Grower
on the grove listed above and on all other land now or hereafter owned by the
Grower or in the Grower's possession as tenant, except avocados that are
retained for the Grower's personal use or consumption and except avocados of
such varieties that Calavo notifies the Grower are not economical to handle
because of the character, quantity or marketability of the fruit. Except as
described in the preceding sentence, Calavo will market, when and where
feasible, all of the avocados grown by the Grower.

     Delivery of the avocados will be made at the Grower's expense and risk of
loss and at the time and place and in the manner reasonably specified by the
Grower, including, without limitation, through the Grower's right to require
Calavo to obtain possession of the avocados at the Grower's grove. Title to the
avocados will pass to Calavo only on the date that it obtains actual possession
of the avocados.

     Calavo has the right to inspect the Grower's groves for crop estimating and
harvesting purposes during reasonable hours. The Grower will assist Calavo in
preparing an annual crop forecast. Calavo has full control of grading, sizing
and weight standards. The Grower will comply with all applicable laws and
regulations regarding the production, harvesting and delivery of the avocados.

2. Term

     The term of this Agreement will be for one year from the effective date and
will automatically renew on a year-to-year basis unless either party gives
written notice of termination of this Agreement at least thirty days prior to
the applicable anniversary of the effective date. Calavo may also terminate this
Agreement upon written notice to the Grower if the Grower is in breach of this
Agreement and fails to correct the breach within ten days after receipt of
written notice of the breach from Calavo. If the Grower engages in a bona fide
sale or lease to a third party of the grove(s) that is subject to this
Agreement, this Agreement will terminate as to such grove(s) on the effective
date of the sale or lease if (i) the Grower provides Calavo with satisfactory
written evidence of the bona fide nature of the sale or lease and (ii) all of
the Grower's obligations hereunder have been satisfied prior to the sale or
lease (including the obligation to deliver all avocados harvested prior to the
sale or lease). Subject to the preceding sentence,
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this Agreement is binding upon the successors and assigns of the Grower and
Calavo, although neither party has the right to assign its obligations to
another person or entity. No termination of this Agreement will release either
party from liability for breaches of this Agreement, and the provisions
described below in Sections 4 and 7 to 9 will survive the termination of this
Agreement.

3. Marketing

     Calavo will receive, pack, market and sell the avocados delivered by the
Grower, at such prices and terms, in such form, and at such times as in its
judgment and discretion it deems best, and will pay the Grower as payment in
full the net proceeds received from the marketing of the avocados less a packing
and marketing fee established by its Board of Directors. The packing and
marketing fee will include, but is not limited to, the costs of receiving,
processing, manufacturing, handling, transporting, advertising, promoting, and
other costs of marketing and administrative costs, and will also include a
profit to Calavo. The avocados may be pooled in one or more pools established by
the Board of Directors and will not be identified to the Grower once they are
graded. Packing and marketing of the avocados will be under the exclusive
control of Calavo.

4. Liens

     Calavo is hereby given a first lien upon all sales proceeds as security for
any and all amounts of any nature owed by the Grower to Calavo, and Calavo may
offset amounts due Calavo against amounts owed to the Grower under this
Agreement. Such rights of Calavo will not be barred by the running of any
statute of limitations, and such rights may be subordinated by appropriate
written instructions when authorized by the Board of Directors in its sole
discretion. The Grower will execute and deliver any documents requested by
Calavo to implement or perfect its rights under this Agreement.

5. Labor

     Calavo will have no control whatsoever over the labor relations policies or
conduct or direction of labor relations of the Grower, nor will the Grower have
any control over Calavo's labor policies.

6. Consignment

     The Grower acknowledges that Calavo may reconsign the avocados to another
party.

7. Notices; Entire Agreement; Severability

     All notices to either the Grower or Calavo will be delivered in writing,
either personally, by facsimile transmission or by registered, certified or
express mail, return receipt requested, postage prepaid, to the address for such
party specified above or to such other address as the party may from time to
time advise the other party, and will be deemed given and received as of actual
personal delivery, on the first business day after the date of delivery shown on
any such facsimile transmission or upon the third business day after deposit in
the U.S. Mail if registered, certified or express mail is used, as the case may
be.

     This Agreement constitutes the entire agreement of the Grower and Calavo
regarding the subject matter hereof and supersedes all prior agreements and
understandings pertaining to such subject matter. This Agreement may be amended
only by a writing signed by the Grower and Calavo.

     If any provision of this Agreement is determined by a duly appointed
arbitrator or a court of competent jurisdiction to be invalid or unenforceable,
the remaining provisions of this Agreement shall continue in full force and
effect.

8. Remedies for Grower's Breach

     The Grower's failure to deliver avocados as required by this Agreement will
result in injury to Calavo, and it would be extremely difficult and
impracticable to fix the amount of damages that Calavo will incur. Therefore,
the Grower agrees to pay to Calavo, upon Calavo's demand, the following amounts
as liquidated
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damages for all avocados that are withheld, delivered, sold, consigned or
otherwise marketed by or for the Grower other than in accordance with the terms
of this Agreement:

          (a) $1,000; plus

          (b) An amount equal to Calavo's packing and marketing fee per pound of
     avocados that is in effect as of the date of the Grower's breach of this
     Agreement, multiplied by the pounds of avocados that were withheld,
     delivered, sold, consigned or otherwise marketed by or for the Grower other
     than in accordance with the terms of this Agreement.

     The foregoing right to recover liquidated damages is in addition to all
other remedies available to Calavo under applicable law including, without
limitation, the right to obtain injunctive relief, and all such remedies are
cumulative and not exclusive.

9. Governing Law; Enforcement of Agreement

     This Agreement is governed by the internal laws of the State of California.
All disputes concerning this Agreement will be settled by arbitration, before
one arbitrator, in accordance with the commercial arbitration rules of the
American Arbitration Association then in effect. The arbitrator will be selected
in accordance with such commercial arbitration rules. A party is entitled to
initiate an arbitration proceeding if a dispute cannot be resolved amicably
within ten days after the other party has been notified of the existence of the
dispute. The arbitrator is authorized to grant injunctive relief and/or specific
performance in addition to monetary relief. The arbitrator hereby is instructed
to interpret and enforce this Agreement in accordance with its terms. All
arbitration proceedings will be held in Los Angeles, California. Notwithstanding
the foregoing, each party is entitled to bring an action for temporary or
preliminary injunctive relief at any time in any court of competent jurisdiction
in order to prevent immeasurable and irreparable injury that might result from a
breach of this Agreement that occurs prior to the conclusion of an arbitration
proceeding.

     The award of the arbitrator in any arbitration proceeding will be final and
may be enforced in any court of competent jurisdiction, and an action to compel
arbitration may be brought in any court of competent jurisdiction. The
unsuccessful party to any arbitration proceeding or to any court action that is
permitted by this Agreement will pay to the successful party all costs and
expenses, including, without limitation, reasonable attorneys' fees and the fees
of the arbitrator, incurred therein by the successful party. EACH PARTY AGREES
THAT ALL RIGHTS TO A TRIAL BY A JURY OF ANY CLAIM CONCERNING THIS AGREEMENT ARE
ABSOLUTELY AND FOREVER WAIVED.

DATED:  ________________________________  CALAVO GROWERS, INC.

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

                                          Title:
                                             -------------------------------

                                          [Name of Grower]

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

                                          Title:
                                             -------------------------------

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