Exhibit 10.4

THIS WARRANT AND THE SECURITIES  ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN
REGISTERED  UNDER THE SECURITIES ACT OF 1933. THEY MAY NOT BE SOLD,  OFFERED FOR
SALE,  PLEDGED,  HYPOTHECATED,  OR OTHERWISE  TRANSFERRED  EXCEPT PURSUANT TO AN
EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933, OR AN OPINION
OF COUNSEL  SATISFACTORY TO THE COMPANY THAT  REGISTRATION IS NOT REQUIRED UNDER
SUCH ACT OR UNLESS SOLD PURSUANT TO RULE 144 UNDER SUCH ACT.


                             STOCK PURCHASE WARRANT


         This Stock  Purchase  Warrant (this  "Warrant"),  dated May 5, 2005, is
issued to Frost National Bank,  Custodian,  FBO Renaissance US Growth Investment
Trust  PLC,  Trust  No.  W00740100,  a  Texas  corporation  (the  "Holder"),  by
Integrated Security Systems, Inc., a Delaware corporation (the "Company").

         1.     Purchase  of  Shares.   Subject  to  the  terms  and  conditions
hereinafter set forth, the Holder is entitled, upon surrender of this Warrant at
the principal office of the Company (or at such other place as the Company shall
notify the holder hereof in writing), to purchase from the Company 514,706 fully
paid and  non-assessable  shares of Common  stock,  no par  value  (the  "Common
Stock"), of the Company (as adjusted pursuant to Section 7 hereof, the "Shares")
for the purchase price specified in Section 2 below.

         2.     Purchase  Price.  The purchase price for the Shares is $0.34 per
share.  Such price shall be subject to  adjustment  pursuant to Section 7 hereof
(such  price,  as  adjusted  from  time to time,  is herein  referred  to as the
"Warrant Price").

         3.     Exercise Period. This Warrant is exercisable in whole or in part
at any time from the date hereof through May 5, 2010.

         4.     Method of Exercise.  While this Warrant remains  outstanding and
exercisable  in accordance  with Section 3 above,  the Holder may  exercise,  in
whole or in part, the purchase rights evidenced  hereby.  Such exercise shall be
effected by:

                (a)  surrender of this  Warrant,  together  with a duly executed
         copy of the form of Exercise Notice attached  hereto,  to the Secretary
         of the Company at its principal officer, and the payment to the Company
         of an amount equal to the  aggregate  purchase  price for the number of
         Shares being purchased; or

                (b) if the Company's  Common Stock is publicly traded as of such
         date,  the  instruction  to retain that number of Shares having a value
         equal to the  aggregate  exercise  price of the Shares as to which this
         Warrant is being  exercised and to issue to the Holder the remainder of
         such Shares computed using the following formula:

                                   Y(A-B)
                               X = ------
                                     A

         Where:  X = the  number of  shares of Common  Stock to be issued to the
         Holder.


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         Y = the number of shares of Common  Stock as to which  this  Warrant is
         being exercised.

         A = the fair market value of one share of Common Stock.

         B = the Warrant Price.

                As used  herein,  the "fair  market value of one share of Common
         Stock" shall mean:

                       (1) Except in the  circumstances  described in clause (2)
                or (3) hereof,  the closing price of the Company's Common Stock,
                as  reported  in the WALL  STREET  JOURNAL,  on the  trading day
                immediately prior to the date of exercise;

                       (2) If such  exercise  is in  conjunction  with a merger,
                acquisition,  or  other  consolidation  pursuant  to  which  the
                Company is not the surviving  entity,  the value received by the
                holders of the Common  Stock  pursuant to such  transaction  for
                each share; or

                       (3) If such exercise is in  conjunction  with the initial
                public  offering of the  Company,  the price at which the Common
                Stock is sold to the public in such offering.

         5.     Certificates  for  Shares.  Upon the  exercise  of the  purchase
rights  evidenced by this Warrant,  one or more  certificates  for the number of
Shares so purchased  shall be issued as soon as practicable  thereafter,  and in
any event within thirty (30) days of the delivery of the subscription notice.

         6      Reservation of Shares. The Company covenants that it will at all
times keep available such number of authorized  shares of its Common Stock, free
from all  preemptive  rights with respect  thereto,  which will be sufficient to
permit the  exercise of this  Warrant  for the full  number of Shares  specified
herein. The Company further covenants that such Shares,  when issued pursuant to
the exercise of this Warrant,  will be duly and validly  issued,  fully paid and
non-assessable  and free from all taxes,  liens and charges  with respect to the
issuance thereof.

         7.     Adjustment of Warrant Price and Number of Shares. The number and
kind of  securities  purchasable  upon  exercise of this Warrant and the Warrant
Price shall be subject to adjustment from time to time as follows:

                (a)  Stock  Dividends,  Subdivisions,   Combinations  and  Other
         Issuances.  If the Company shall at any time prior to the expiration of
         this Warrant  subdivide its Common Stock,  by stock split or otherwise,
         combine its Common Stock or issue additional shares of its Common Stock
         as a dividend  with  respect to any  shares of its  Common  Stock,  the
         number  of  Shares  issuable  on the  exercise  of this  Warrant  shall
         forthwith be proportionately  increased in the case of a subdivision or
         stock  dividend  and  proportionately   decreased  in  the  case  of  a
         combination. Appropriate adjustments shall also be made to the purchase
         price payable per share,  but the aggregate  purchase price payable for
         the total number of Shares purchasable under this Warrant (as adjusted)
         shall  remain the same.  Any  adjustment  under this Section 7(a) shall
         become  effective at the close of business on the date the  subdivision
         or  combination  becomes  effective  or as of the  record  date of such
         dividend,  or, in the  event  that no  record  date is fixed,  upon the
         making of such dividend.


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                (b)   Reclassification,    Reorganization,   Merger,   Sale   or
         Consolidation.   In  the   event  of  any   reclassification,   capital
         reorganization  or other  change  in the  Common  Stock of the  Company
         (other than as a result of a subdivision, combination or stock dividend
         provided  for in Section (a) above) or in the event of a  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 the  connection  therewith  consideration  is  payable  to
         holders of Common Stock in cash, securities or other property,  then as
         a  condition  of  such  reclassification,   reorganization  or  change,
         consolidation, merger or sale, lawful provision shall be made, and duly
         executed  documents  evidencing  the  same  shall be  delivered  to the
         Holder,  so that the  Holder  shall have the right at any time prior to
         the  expiration of this Warrant to purchase,  at a total price equal to
         that payable upon the  exercise of this  Warrant  immediately  prior to
         such event,  the kind and amount of cash,  securities or other property
         receivable in connection with such reclassification,  reorganization or
         change,  consolidation,  merger or sale, by a holder of the same number
         of shares of Common Stock as were exercisable by the Holder immediately
         prior   to   such    reclassification,    reorganization   or   change,
         consolidation, merger or sale. In any such case, appropriate provisions
         shall be made with  respect to the rights and interest of the Holder 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 Holder shall be entitled to receive
         distributions  on the date of such event on an equal basis with holders
         of Common Stock as if this Warrant had been exercised immediately prior
         to such event, less the Warrant Price. Upon receipt of such payment, if
         any,  the  rights of the Holder  shall  terminate  and cease,  and this
         Warrant 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 Warrant, make payment
         by delivering a check in such amount as is appropriate (or, in the case
         of  consideration  other than  case,  such  other  consideration  as is
         appropriate)  to such  person as it may be  directed  in writing by the
         Holder surrendering this Warrant.

                (c)  Certain  Distributions.  In case the  Company  shall  fix a
         record  date for the  making of a  dividend  or  distribution  of cash,
         securities  or property to all holders of Common Stock  (excluding  any
         dividends or distributions  referred to in Sections 7(a) or 7(b) above,
         the number of Shares purchasable upon an exercise of this Warrant after
         such record  date shall be  adjusted  to equal the product  obtained by
         multiplying the number of Shares  purchasable  upon an exercise of this
         Warrant  immediately  prior  to such  record  date by a  fraction,  the
         numerator of which shall be the Warrant Price immediately prior to such
         distribution,  and the  denominator of which shall be the Warrant Price
         immediately prior to such distribution,  less the fair market value per
         Share, as determined by the Holder, of the cash, securities or property
         so distributed. Such adjustment shall be made successively whenever any
         such  distribution is made and shall become  effective on the effective
         date of distribution.

         8.     Pre-Exercise  Rights.  Prior to  exercise of this  Warrant,  the
Holder shall not be entitled to any rights of a shareholder  with respect to the
Shares,  including without  limitation,  the right to vote such Shares,  receive
preemptive rights or be notified of shareholder  meetings,  and the Holder shall
not be entitled to any notice or other communication  concerning the business or
affairs of the Company.

         9.     Restricted Securities.  The Holder understands that this Warrant
and the Shares purchasable  hereunder constitute  "restricted  securities" under
the federal  securities  laws inasmuch as they are being,  or will be,  acquired
from the Company in transactions not involving a public offering and accordingly
may not,  under such laws and applicable  regulations,  be resold or transferred
without  registration  under  the  Securities  Act of 1933,  as  amended,  or an
applicable  exemption  from  registration.   In  this  connection,   the  Holder
acknowledges that Rule 144 of the Securities and Exchange Commission is not now,
and may not in the  future be,  available  for  resales of the Shares  purchased
hereunder.  The  Holder  further  acknowledges  that the  Shares  and any  other
securities   issued  upon   exercise  of  this  Warrant   shall  bear  a  legend
substantially in the form of the legend appearing on the face hereof.

         10.    Certification   of   Investment   Purpose.   Unless  a   current
registration statement under the Securities Act of 1933, as amended, shall be in
effect  with  respect  to the  securities  to be issued  upon  exercise  of this
Warrant,  the Holder  hereof,  by accepting  this Warrant,  covenants and agrees
that, at the time of exercise  hereof,  the Holder will deliver to the Company a
written  certification that the securiti4es  acquired by the Holder are acquired
for  investment  purposes only and that such  securities are not acquired with a
view to, or for sale in connection with, any distribution thereof.

         11.    Successors and Assigns. The terms and provisions of this Warrant
shall inure to the benefit of, and be binding  upon,  the Company and the Holder
and their respective successors and assigns.

         13.    Governing Law. This Warrant shall be governed by the laws of the
State of Texas, excluding the conflicts of laws provisions thereof.

                                       INTEGRATED SECURITY SYSTEMS, INC.



                                       By: /S/ C. A. RUNDELL, JR.
                                           ----------------------
                                           C. A. Rundell, Jr.
                                           Chairman and Chief
                                           Executive Officer



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<PAGE>

                                 EXERCISE NOTICE


                                                   Dated ______________, _______

         The  undersigned  hereby  irrevocably  elects  to  exercise  the  Stock
Purchase Warrant, dated May 5, 2005 issued by Integrated Security Systems, Inc.,
a Delaware  corporation  (the  "Company")  to the  undersigned  to the extent of
purchasing  _______________  shares of Common Stock and hereby makes  payment of
$____________ in payment of the aggregate Warrant Price of such Shares.

                           RENAISSANCE US GROWTH INVESTMENT TRUST FUND PLC


                           By: ___________________________________











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