Exhibit 99.3

                                                           EXECUTION COPY

                               SECURITY AGREEMENT

         THIS SECURITY AGREEMENT (this "AGREEMENT") is executed by NUMEREX CORP.
("NUMEREX"), NUMEREX INVESTMENT CORP. ("NI"), NUMEREX SOLUTIONS LLC ("NS"), DCX
SYSTEMS, INC. ("DCX"), BNI SOLUTIONS LLC ("BNI"), BROADBAND NETWORKS, INC.
("BROADBAND"), MOBILE GUARDIAN LLC ("MG"), DATA1SOURCE LLC ("DATA1SOURCE"),
CELLEMETRY LLC ("CELLEMETRY") and UPLINK SECURITY, INC. ("UPLINK" and,
collectively with NI, NS, DCX, BNI, Broadband, MG, Cellemetry and Uplink, the
"SUBSIDIARIES", and the Subsidiaries together with Numerex, "DEBTORS") in favor
of BELLSOUTH PERSONAL COMMUNICATIONS, LLC, a wholly owned subsidiary of CINGULAR
WIRELESS LLC ("SECURED PARTY").

         For good and valuable consideration, the receipt and sufficiency of
which is hereby acknowledged:

     1.  SECURITY INTEREST. Except as set forth in this SECTION 1, each of the
         Debtors hereby grants, assigns, transfers, pledges and conveys to
         Secured Party, a present and continuing security interest in and lien
         on all now existing or hereafter arising rights, titles and interests
         of Debtors in, to or under any and all of their respective assets,
         including all inventory, machinery, equipment, accounts, contract
         rights and general intangibles (the "DEBTORS' ASSETS"), and Numerex and
         NI hereby grant, assign, transfer, pledge and conveys to Secured Party
         all stock certificates and membership units of the Subsidiaries owned
         by Numerex and NI in the Subsidiaries (the "PLEDGED SHARES"), in each
         case together with all substitutions, replacements, products and
         proceeds of each of the foregoing (including cash and non-cash)
         (collectively, the "PROCEEDS"; Debtors' Assets, Pledged Shares and the
         Proceeds are hereinafter referred to collectively as the "COLLATERAL").
         Numerex and Secured Party each acknowledge and agree that the
         Collateral hereunder shall not include any of the assets or stock
         certificates of Numerex's subsidiary, Digilog, Inc., a Pennsylvania
         corporation.

     2.  SECURED LIABILITIES. This Agreement and the security interest and lien
         granted hereby to Secured Party secures the payment of all obligations
         of Numerex to Secured Party arising under that certain Secured
         Promissory Note of even date herewith (the "NOTE"), executed and issued
         by Numerex in favor of Secured Party (the "OBLIGATIONS").

     3.  REPRESENTATIONS, WARRANTIES, COVENANTS AND AGREEMENTS OF DEBTORs. Each
         of the Debtors hereby represents, warrants, covenants and agrees that:
         (A) it is a corporation or



         a limited liability company, as applicable, duly organized, validly
         existing and in good standing under the laws of the state of its
         incorporation or formation; (B) it has all requisite corporate or
         limited liability company, as applicable, power and authority, and has
         obtained all approvals and consents necessary, to execute, deliver and
         perform this Agreement; (C) the execution, delivery and performance of
         this Agreement have been duly authorized by all requisite corporate or
         limited liability company action, as applicable, on its part; (D) this
         Agreement constitute its valid, legal and binding obligation and is
         enforceable against it in accordance with the terms hereof and grants
         to Secured Party a valid and enforceable security interest in or other
         lien in the Collateral; (E) it has good and marketable title to the
         respective Collateral owned or leased by it (or in the case of any
         after-acquired Collateral, it will have good and marketable title to
         the respective Collateral owned or leased by it at the time it acquires
         rights in such Collateral); (F) except for the security interest and
         lien granted hereby in favor of Secured Party by Debtors, it is, or to
         the extent of any Collateral acquired after the date hereof, will be,
         the owner or holder of the Collateral free from any adverse lien,
         security interest or encumbrances except liens, security interests or
         encumbrances that are expressly subordinate to the rights of Secured
         Party; (G) any and all records concerning the respective Collateral
         owned or leased by it will be kept at its principal address indicated
         below; (H) all records with respect to the Collateral at any time
         furnished by it to Secured Party are and will be true and correct as of
         the date furnished; (I) it hereby authorizes Secured Party to file UCC
         Financial Statements evidencing the security interest and lien granted
         by it hereby; (J) all risk of loss of the Collateral shall at all time
         be and remain upon it irrespective of whether such Collateral is then
         in its or Secured Party's possession; (K) it shall do all acts that may
         be necessary to maintain, preserve and protect the respective
         Collateral owned or leased by it, including appear in and defend any
         action or proceeding that may adversely affect its title to or Secured
         Party's interest in the Collateral; (L) it shall not use or permit any
         Collateral owned or leased by it to be used in violation of any
         applicable law, rule, or regulation or any provision of this Agreement,
         the Stock Purchase Agreement or the Note; (M) it shall pay promptly
         when due all taxes, assessments, charges and liens now or hereafter
         imposed upon or affecting the Collateral owned or leased by it; (N) it
         shall not sell, encumber, lease, rent or otherwise dispose of or
         transfer any Collateral owned or leased by it, or any right or interest
         therein, except as expressly provided in SECTION 4 below; (N) upon the
         occurrence and during the continuance of an Event of Default (as
         defined below), Numerex shall reimburse Secured Party upon demand for
         all costs and expense, including, without limitation, reasonable
         attorneys' fees and disbursements, Secured Party may now or hereafter
         incur while exercising or enforcing any right, power or remedy provided
         to Secured Party by this Agreement or by law, all of which costs and
         expenses shall constitute part of the Obligations secured hereunder;
         (O) upon request of Secured Party, it will do all acts and things, and
         will execute all instruments (including security agreement, financing
         statements, amendments, statements of change, etc.) necessary under
         applicable law to establish, maintain and continue Secured Party's
         perfected security interest in the Collateral; and (P) it will
         immediately give written notice to Secured Party of any change in its
         name, state of incorporation or principal place of business.



     4.  ADMINISTRATION OF COLLATERAL. Unless and until an Event of Default
         shall have occurred and be continuing, each Debtor may manage, collect
         and administer the Collateral (including, without limitation, voting
         its interests in the Pledged Shares, and collecting and retaining all
         dividends and distributions made in respect thereof) only in the
         ordinary course of its business, and consistent with its past practices
         and covenants and obligations hereunder. Provided that no Event of
         Default has occurred, in no event shall any Debtor have a right to
         sell, transfer, assign, convey or otherwise dispose of (a "SALE") any
         of the Collateral owned or leased by it without prior written consent
         of Secured Party, which consent could not be unreasonably withheld.
         Notwithstanding the foregoing and subject to the requirements below,
         Secured Party hereby consents to (i) a Sale by Numerex of all of its
         ownership interest in DCX, BNI, Broadband and Data1Source, and (ii) a
         Sale by DCX, BNI and Data1Source of all of their respective assets, in
         each case in any one or more transactions (individually, an "INDIVIDUAL
         PERMITTED SALE", and collectively, the "PERMITTED SALE"), provided that
         the consideration received by Numerex or any other Debtor as a result
         of each Individual Permitted Sale is paid in cash. To the extent any
         Individual Permitted Sale is proposed which includes any consideration
         other than cash, such Individual Permitted Sale will require the
         consent of the Secured Party, which consent will not be unreasonably
         withheld; provided, however, that Secured Party shall retain a security
         interest in the proceeds of any such Sale regardless of the type of
         consideration received thereunder. The Permitted Sale shall also be
         subject to the mandatory prepayment provisions contained in the Note.

     5.  PERFORMANCE OF DEBTORS' OBLIGATIONS. Upon occurrence or during the
         continuance of an Event of Default, in addition to and not in
         limitation of all the rights under SECTION 7 below, Secured Party may,
         at its sole discretion, take any action that is necessary for the
         maintenance or preservation of any of the Collateral or its interest
         therein.

     6.  EVENT OF DEFAULT. An "EVENT OF DEFAULT" shall mean (A) each Event of
         Default under the Note; (B) material breach by any Debtor of any
         representation or warranty made by it in SECTION 3 of this Agreement;
         (C) failure of any Debtor to perform or comply with, in any material
         respect, any of its covenants set forth in SECTION 3 of this Agreement,
         which failure is not cured within twenty (20) days of the giving by
         Secured Party to such Debtor of written notice of same; (D) failure of
         any Debtor to perform and comply with any other covenants set forth in
         this Agreement, including covenants in SECTION 4; or (E) if all or any
         material portion of the Collateral is seized or levied upon or a
         receiver or other custodian is appointed for it.

     7.  REMEDIES UPON DEFAULT. If an Event of Default shall occur and be
         continuing, then Secured Party may: (A) declare any or all of the
         Obligations to be immediately due and payable and foreclose or
         otherwise enforce Secured Party's security interest in or other lien
         hereunder on any or all of the Collateral in any manner permitted by
         law or provided for in this Agreement; (B) sell or otherwise dispose of
         any of the Collateral; (C) demand that any Debtor assemble the records
         relating to the Collateral owned by it and make them available to
         Secured Party at a place designated by Secured Party which is
         reasonably convenient for Secured Party and such Debtor; (D) instruct
         any Debtor in writing to deliver to Secured Party, upon such Debtor's
         receipt thereof, all cash, checks,



         drafts, chattel paper and other instruments in writing for the payment
         of money (properly endorsed, where required, so that such items may be
         collected by Secured Party) that are thereafter received by such Debtor
         in full or partial payment or otherwise as proceeds of any of the
         Collateral; (E) collect all accounts receivable, including, without
         limitation, notifying the account debtors in its name or in the name of
         any Debtor, as its attorney-in-fact, to make payments directly to
         Secured Party; and (F) exercise all other rights of a secured party
         under the UCC (as defined below).

     8.  EXPENSES INCURRED BY SECURED PARTY. In the Secured Party's reasonable
         discretion, if any Debtor fails to do so, the Secured Party may
         discharge taxes and other encumbrances at any time levied or placed on
         any of the Collateral, maintain any of the Collateral and pay any
         necessary filing fees or insurance premiums. Numerex agrees to
         reimburse the Secured Party on demand for all expenditures so made. The
         Secured Party shall have no obligation to Debtors or any other person
         to make any such expenditures, nor shall the making thereof be
         construed as a waiver or cure of any Event of Default.

     9.  SURETYSHIP WAIVERS BY DEBTORS. The Debtors waive demand, notice,
         protest, notice of acceptance of this Agreement, notice of loans made,
         credit extended, Collateral received or delivered or other action taken
         in reliance hereon and all other demands an notices of each
         description. With respect to both the Obligations and the Collateral,
         the Debtors assent to any extension or postponement of the time of
         payment or any other indulgence, to any substitution, exchange or
         release of or failure to perfect any security interest in any
         Collateral, to the addition or release of any party or person primarily
         or secondarily liable, to the acceptance of partial payment thereon and
         the settlement, compromising or adjusting of any thereof, all in such
         manner and at such time or times as the Secured Party may deem
         advisable. The Secured Party, to the extent allowed by law, shall have
         no duty as to the collection or protection of the Collateral or any
         income therefrom, the preservation of rights against prior parties, or
         the preservation of any rights pertaining thereto. The Debtors further
         waive any and all other suretyship defenses.

     10. PROCEEDS OF DISPOSITIONS; EXPENSES. Upon the occurrence and during the
         continuance of an Event of Default, the Debtors agree to pay to Secured
         Party on demand any and all expenses, including reasonable attorneys'
         fees and disbursements, incurred or paid by the Secured Party in
         protecting, preserving or enforcing the Secured Party's rights and
         remedies under or in respect of any of the Obligations or any of the
         Collateral. After deducting all of said expenses, the residue of any
         proceeds of collection or sale or other disposition of Collateral
         shall, to the extent actually received in cash, be applied to the
         payment of the Obligations in such order or preference as Secured Party
         may determine. Upon the final payment and satisfaction in full of all
         of the Obligations and after making any payments required by Sections
         9-608(a)(1)(C) or 9-615(a)(3) of the Uniform Commercial Code of the
         State of Georgia, any excess shall be returned to the Debtors. In the
         absence of final payment and satisfaction in full of all of the
         Obligations, the Debtors shall remain liable for any deficiency.

     11. NOTICE OF INTENDED DISPOSITION. If any notification of intended
         disposition of any Collateral is required by law, reasonable
         notification shall be deemed given if written



         notice is either given by express courier or deposited in the U.S.
         Mail, certified postage prepaid, addressed to Debtors and such other
         persons or entities as Secured Party deems to be appropriate, stating
         the time and place of any public sale or the time after which any
         private sale or disposition is to be made, at least twenty (20) days
         prior thereto.

     12. MISCELLANEOUS. (A) This Agreement may be executed simultaneously in two
         or more counterparts, each of which shall be deemed to be an original,
         but all of which together shall constitute one agreement; (B) this
         Agreement shall in all respects be construed in accordance with and
         governed by the laws of the state of Georgia without regard to the
         conflicts of laws principles thereof; (C) the captions of the sections
         of this Agreement are inserted for convenience only and shall not be
         deemed to constitute a part hereof or used in construing the intent of
         the parties; (D) if any part of any provision of this Agreement shall
         be invalid or unenforceable under applicable law, said part shall be
         ineffective to the extent of such invalidity only, without in any way
         effecting the remaining parts of said provision or the remaining
         provisions; (E) this Agreement shall not be modified or amended except
         in writing signed by each of the parties hereto; (F) this Agreement
         shall bind and inure to the benefit of the parties, their successors,
         legal representatives, heirs and, where permitted, assigns; (G) this
         Agreement may be executed in any number of counterparts, each of which
         when so executed shall be deemed to be an original and all of which
         taken together shall constitute one and the same instrument; (H) TIME
         IS OF THE ESSENCE; (I) any waiver, forbearance or delay by Secured
         Party in exercising any of its right, powers or remedies hereunder
         shall not preclude the further exercise thereof, and every right, power
         or remedy of Secured Party hereunder shall continue in full force and
         effect until such right, power or remedy is specifically waived in
         writing executed by Secured Party; (J) this Agreement, the Note and the
         Stock Purchase Agreement contain the entire agreement between Secured
         Party and Debtors with respect to the Collateral and the Obligations
         and supersedes all prior agreements, commitments, understandings,
         negotiations or correspondence between them with respect thereto; (K)
         the rights, powers and remedies of Secured Party under this Agreement
         shall be in addition to and not in limitation of all other rights,
         powers or remedies given to Secured Party by applicable law and the
         Note, all of which rights, powers, and remedies shall be cumulative and
         may be exercised successively or concurrently without impairing Secured
         Party's security interest in or other lien on any of the Collateral;
         (L) Secured Party may assign or transfer this Agreement, but this
         Agreement shall not be assignable or transferable, in whole or in part,
         by any Debtor without the prior written consent of Secured Party; (M)
         all notices or communications shall be given to Debtors at the
         addresses set forth below following the caption "Principal Address" and
         shall be given to Secured Party at the address set forth below
         following the caption "Address of Secured Party"; and (N) unless
         otherwise specifically provided herein to the contrary, such written
         notices and communications shall be delivered by facsimile, email, and
         hand or overnight courier service, or mailed, postage prepaid,
         addressed to the parties hereto at the addresses referred to above in
         subsection (M) or to such other addresses as any party may designate to
         the other party by a written notice given in accordance with the
         provisions hereof. Any written notice delivered by facsimile or email
         shall be deemed given upon transmission. Any notice delivered by hand
         or by overnight courier service shall be deemed given or received



         upon receipt. As used herein, the "UCC" shall mean the Uniform
         Commercial Code, as enacted in the State of Georgia, and as amended
         from time to time. Capitalized terms used but not defined herein
         (including, without limitation, the descriptions of the Collateral in
         SECTION 1 hereof) shall have the meanings given to them in the UCC.

     13. JURY WAIVER. EACH OF THE DEBTORS AND SECURED PARTY HEREBY KNOWINGLY,
         VOLUNTARILY, INTENTIONALLY AND IRREVOCABLY WAIVE TO THE FULLEST EXTENT
         PERMITTED BY APPLICABLE LAW, THE RIGHT ANY OF THE PARTIES MAY HAVE TO A
         TRIAL BY JURY IN RESPECT TO ANY LITIGATION, WHETHER IN CONTRACT OR
         TORT, AT LAW OR IN EQUITY, BASED HEREON, OR ARISING OUT OF, UNDER OR IN
         CONNECTION WITH THIS AGREEMENT, THE COLLATERAL, THE OBLIGATIONS SECURED
         HEREBY, AND ANY OTHER DOCUMENT OR INSTRUMENT CONTEMPLATED TO BE
         EXECUTED IN CONJUNCTION HEREWITH, OR ANY COURSE OF CONDUCT, COURSE OF
         DEALING, STATEMENTS (WHETHER VERBAL OR WRITTEN) OR ACTIONS OF ANY PARTY
         HERETO. THIS PROVISION IS A MATERIAL INDUCEMENT FOR SECURED PARTY
         ENTERING INTO THIS AGREEMENT. FURTHER, EACH DEBTOR HEREBY CERTIFIES
         THAT NO REPRESENTATIVE OR AGENT OF SECURED PARTY, NOR SECURED PARTY'S
         COUNSEL, HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SECURED PARTY
         WOULD NOT, IN THE EVEN OF SUCH LITIGATION, SEEK TO ENFORCE THIS WAIVER
         OF RIGHT TO JURY TRIAL PROVISIONS. NO REPRESENTATIVE OR AGENT OF
         SECURED PARTY NOR SECURED PARTY'S COUNSEL HAS THE AUTHORITY TO WAIVE,
         CONDITION, OR MODIFY THIS PROVISION.

     EACH DEBTOR EXPRESSLY AND IRREVOCABLY CONSENTS THAT ANY LEGAL ACTION OR
     PROCEEDING AGAINST IT UNDER, ARISING OUT OF, OR IN ANY MANNER RELATING TO
     THIS AGREEMENT SHALL BE BROUGHT IN THE STATE OR DISTRICT COURTS OF THE
     STATE OF GEORGIA. EACH DEBTOR, BY ITS EXECUTION AND DELIVERY OF THIS
     AGREEMENT, EXPRESSLY AND IRREVOCABLY CONSENTS AND SUBMITS TO THE PERSONAL
     JURISDICTION OF ANY OF SUCH COURTS IN ANY SUCH ACTION OR PROCEEDING AND
     HEREBY EXPRESSLY AND IRREVOCABLY WAIVES ANY CLAIM OR DEFENSE IN ANY SUCH
     ACTION OR PROCEEDING BASED ON ANY ALLEGED LACK OF PERSONAL JURISDICTION,
     IMPROPER VENUE OR FORUM NON CONVENIENS OR ANY SIMILAR BASIS.

                  IN WITNESS WHEREOF, this Agreement has been signed, sealed,
         and delivered by each Debtor on this 28th day of March, 2003.

                                    NUMEREX CORP.

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: Chairman and Chief Executive Officer



                                    NUMEREX INVESTMENT CORP.

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    BNI SOLUTIONS LLC

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    DCX SYSTEMS, INC.

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    NUMEREX SOLUTIONS, LLC

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    BROADBAND NETWORKS, INC.

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    MOBILE GUARDIAN LLC

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    DATA1SOURCE LLC

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President



                                    CELLEMETRY LLC

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

                                    UPLINK SECURITY, INC.

                                    By: /s/ Stratton J. Nicolaides
                                        ----------------------------------------
                                    Name: Stratton J. Nicolaides
                                    Title: President

Principal Address of Numerex:
1600 Parkway Circle
Suite 200
Atlanta, GA 30339

Principal Address of each of the Subsidiaries:
BNI Solutions LLC                                   Numerex Solutions, LLC
2820 E. College Ave.                                1600 Parkwood Circle
Suite B                                             Suite 200
State College, PA 16801-7548                        Atlanta, Georgia 30339-2119

Uplink Security, Inc.                               DCX Systems, Inc.
1600 Parkwood Circle                                2360 Maryland Road
Suite 200                                           Willow Grove, PA 19090
Atlanta, Georgia 30339-2119

Broadband Networks, Inc.                            Mobile Guardian LLC
2820 E. College Ave.                                1600 Parkwood Circle
Suite B                                             Suite 200
State College, PA 16801-7548                        Atlanta, Georgia 30339-2119

Data1Source LLC                                     Numerex Investment Corp.
1600 Parkwood Circle                                1600 Parkwood Circle
Suite 200                                           Suite 200
Atlanta, Georgia 30339-2119                         Atlanta, Georgia 30339-2119

Cellemetry LLC
1600 Parkwood Circle
Suite 200
Atlanta, Georgia 30339-2119



Address of Secured Party:
5565 Glenridge Connector
Suite 2000
Atlanta, Georgia 30342
Facsimile No. 404-236-6324