<PAGE>

                                                                  EXHIBIT 10.23


                               CLOSING AGREEMENT

         THIS CLOSING AGREEMENT ("Closing Agreement") is made and entered into
by and among SDR Metro Inc. (a/k/a SDR Metro Incorporated), an Ohio corporation
("SDR"), Brent Simon ("INVENTOR"), and RadioMetrix, Inc. (a/k/a Radio Metrix
Inc.) ("RADIOMETRIX"), a Florida corporation, as of this 8th day of January
2002.

         WHEREAS, on October 9, 2000 SDR, INVENTOR and RADIOMETRIX entered into
that certain Agreement setting forth the terms and conditions to which SDR and
INVENTOR would sell to RADIOMETRIX or its assigns, and RADIOMETRIX or its
assigns would purchase the PATENT and the PATENT RIGHTS as defined in the
Agreement ("Purchase Agreement"); and

         WHEREAS, pursuant to that certain Extension Agreement entered into by
SDR, INVENTOR and RADIOMETRIX, as of September 25, 2001 ("Extension
Agreement"), the Closing on the aforedescribed purchase is to occur no later
than January 9, 2002; and

         WHEREAS, in accordance with Paragraph 4.b) of the Purchase Agreement,
the parties wish to enter into this Closing Agreement to clarify certain
matters and effectuate the transaction and the conveyance of the PATENT and
PATENT RIGHTS to RADIOMETRIX.

         NOW, THEREFORE, in consideration of the foregoing recitals and of the
mutual promises made herein, and for other good and valuable consideration,
receipt of which is hereby acknowledged by each party, and the parties,
intending to be legally bound, hereby agree as follows:

         1.       SDR, at the closing, shall assign to RADIOMETRIX all its
right, title and interest in and to the License Agreement entered into by and
between SDR and RADIOMETRIX dated as of the 14th day of March 1992 and as
amended by that certain Amendment to License Agreement entered into by the
parties dated February 14, 1997 and May 26, 1998 ("License Agreement"). The
Assignment of License Agreement shall be in the form attached hereto as Exhibit
"A".

         2.       SDR and INVENTOR represent, warrant, confirm, and reaffirm to
RADIOMETRIX and SMARTGATE that:

                  a.       RADIOMETRIX and SDR have each fully met all of their
respective obligations under the License Agreement;

                  b.       Neither SDR nor INVENTOR has any claim or right,
title or interest in or to any improvements or inventions, whether or not the
subject of patent applications, or any proprietary information or trade secrets
that may improve, benefit or augment the TECHNOLOGY (collectively referred to
as "RADIOMETRIX' IMPROVEMENTS TO THE TECHNOLOGY") that RADIOMETRIX or
SmartGate Inc. and SmartGate, L.C. (collectively "SMARTGATE"), the Sublicense
of RADIOMETRIX or their respective employees or associates may have made
since the date of the License Agreement or that may be made in the future,
nor does SDR or INVENTOR have any claim or right, title and interest in or to
any patents or patent applications filed by RADIOMETRIX or SMARTGATE relating to
the PATENT, PATENT RIGHTS or TECHNOLOGY that RADIOMETRIX or SMARTGATE may have
filed since entering into the License Agreement or that may be filed in the
future. SDR and INVENTOR further agree to execute such documents, including
documents of assignment and conveyance as RADIOMETRIX may, in the future,
request which documents shall reflect, agree and confirm that RADIOMETRIX or
its assigns have received all of the right, title and interest of

<PAGE>

                                                                              2



SDR and INVENTOR in and to the PATENT and PATENT RIGHTS, and TECHNOLOGY, and
any and all of RADIOMETRIX' IMPROVEMENTS TO THE TECHNOLOGY past or future;

                  c.       All of the representations and warranties of SDR, as
set forth in Paragraph 6 of the License Agreement, are incorporated into this
Closing Agreement by reference and made an integral part hereof, and remain
true and correct, and are reaffirmed and shall remain true and correct
following the Closing, and shall survive the Closing and payment of the
Promissory Note;

                  d.       INVENTOR is the sole inventor, and SDR is the sole
owner of the PATENT, PATENT RIGHTS and TECHNOLOGY being sold under the
Agreement, and that no other person nor entity has any right, title or
interest in or claim to the PATENT, PATENT RIGHTS or TECHNOLOGY, and should any
person or entity assert any such right, title or interest or claim, SDR and
INVENTOR shall defend and hold RADIOMETRIX harmless with respect to any such
claim, and in the event any such claim is asserted during the period the
Promissory Note remains unpaid, SDR and INVENTOR agree that RADIOMETRIX shall
have the right to set any such claim, cost, expense, recovery or settlement off
against its obligation to pay the Promissory Note;

                  e.       SDR and INVENTOR acknowledge that Samuel S. Duffey
and Duffey & Dolan, P.A. have served as legal counsel only to RADIOMETRIX with
respect to the License Agreement, Purchase Agreement, Extension Agreement, and
this Closing Agreement. SDR and INVENTOR further acknowledge they have each been
advised to and have had the opportunity to seek and rely upon their own counsel
with respect to the License Agreement, Purchase Agreement, Extension Agreement
and this Closing Agreement and that neither SDR nor INVENTOR has received nor
relied upon any legal advice from RADIOMETRIX' legal counsel.

                  f.       SDR has full and complete authority to enter into
and close the Purchase Agreement and to execute and deliver the Assignment,
Assignment of License Agreement and this Closing Agreement.

                  g.       Attached, are true and correct copies of Minutes of
a Meeting of Stockholders and Directors of SDR, which meeting was duly and
legally conducted and which authorized and approved the Purchase Agreement,
this Closing Agreement, the Assignment, Assignment of License Agreement and all
transactions and actions reflected therein, and expressly authorized SDR's
officers to execute, deliver and carry out the intentions of said agreements
and documents.

                  h.       Neither SDR nor INVENTOR require the consent or
approval of any third party to enter into the Purchase Agreement, this Closing
Agreement, the Assignment or the Assignment of License Agreement and the
execution of such documents will not violate or breach any agreement or
obligation to which SDR or INVENTOR is a party.

                  i.       The correct corporate name of SDR is SDR Metro Inc.
The License Agreement, Purchase Agreement and Extension to the Purchase
Agreement each contained a typographical error which referred to SDR as SDR
Metro Incorporated. SDR expressly acknowledges that the reference to SDR Metro
Incorporated means SDR Metro Inc. and each of said documents are hereby
ratified in full. This Closing Agreement and all of the closing documents under
the Purchase Agreement shall reflect the proper name of SDR (i.e., - SDR Metro
Inc.)


<PAGE>
                                                                              3



         3.       RADIOMETRIX represents, warrants, confirms, and reaffirms to
SDR and INVENTOR that:

                  a.       RADIOMETRIX' obligation to deliver the cash portion
of the purchase price and its obligations to pay the Promissory Note in
accordance with its terms, and its obligations under Security Agreement
establishing SDR's security interest in the PATENT and pledging the PATENT as
collateral for payment of the Promissory Note is hereby reaffirmed;

                  b.       The correct corporate name of RADIOMETRIX is Radio
Metrix Inc. The License Agreement, Purchase Agreement and Extension to the
Purchase Agreement each contained typographical errors which referred to
RADIOMETRIX as Radio Metrix Incorporated or Radio Metrix, Inc. RADIOMETRIX
expressly acknowledges that the reference to Radio Metrix Incorporated or Radio
Metrix, Inc. means Radio Metrix Inc. and each of said documents are hereby
ratified in full. This Closing Agreement and all of the closing documents under
the Purchase Agreement shall reflect the proper name of RADIOMETRIX (i.e. -
Radio Metrix Inc.)

         4.       The parties agree that as an additional closing document in
accordance with Paragraph 4.b) of the Purchase Agreement, SDR shall, as
requested by Patent Attorney, Thomas E. Anderson, execute at Closing the
Assignment for recordation in the Patent Office as attached hereto as Exhibit
"B".

         5.       This Closing Agreement is a supplement to the Purchase
Agreement and Extension Agreement and shall be interpreted so as to be
consistent with those agreements, and shall survive the Closing of the purchase
of the PATENT and PATENT RIGHTS.

         6.       Attached as Exhibit "C" is the Promissory Note to be
delivered by RADIOMETRIX to SDR at closing which has been revised from the
form of Note attached to the Purchase Agreement to reflect: (i) Radio Metrix
Inc. as the Maker instead of "Radio Metrix, Inc."; (ii) SDR Metro Inc. as Payee
instead of "SDR Metro Incorporated"; and (iii) to reference the Remedy Upon
Default Agreement.

         7.       RADIOMETRIX and INVENTOR agree that with respect to a
consulting relationship between RADIOMETRIX and INVENTOR, it is the parties
intention to negotiate and enter into a formal consulting agreement, and until
such time, the terms of the consulting relationship shall be as set forth in
that certain Memo from RADIOMETRIX to INVENTOR dated August 28, 2000 and
attached hereto as Exhibit "D".

         IN WITNESS WHEREOF, the parties have executed this Closing Agreement
on the day and year first above written.

 SDR Metro Inc.                          Radio Metrix Inc.
 an Ohio corporation                     a Florida corporation



 By:   /s/ David L. E. Jones, President         By:  /s/ S.A. Michael, President
      ---------------------------------             ----------------------------
 Its:                                    Its:  President


 Brent Simon



         /s/ Brent Simon
-----------------------------------


<PAGE>


                        ASSIGNMENT OF LICENSE AGREEMENT

         WHEREAS, SDR METRO Inc., a corporation of the State of Ohio, having
its principal place of business at 27367 Tungsten Road, Euclid, Ohio 44132,
hereinafter called Assignor, is a party to that certain License Agreement
entered into by and between SDR Metro Inc. and Radio Metrix Inc. dated as of
the 14th day of March 1992 and as amended by that certain Amendment to License
Agreement entered into by the parties dated February 14, 1997 and May 26, 1998
("License Agreement") and desires to assign its right, title and interest in
and to the License Agreement to Radio Metrix Inc.

         WHEREAS, Radio Metrix Inc., a corporation of the State of Florida
("Assignee"), having its principal place of business at 4400 Independence Court,
Sarasota, Florida 34234, desires to acquire SDR Metro Inc.'s entire right,
title and interest in and to the License Agreement.

         NOW, THEREFORE, for and in consideration of the sum of One Dollar
($1.00) and other good and valuable considerations, receipt whereof is hereby
acknowledged, Assignor, by these presents, does sell, assign and transfer unto
said Assignee, its successors and assigns, all right, title and interest in the
License Agreement.

         Assignor hereby agrees to execute any and all papers, including
further assignment documents of any and all kinds in any and all countries, and
to perform any and all acts which assignee may deem necessary to secure thereto
the rights herein assigned, sold and set over.


                                   EXHIBIT A


<PAGE>

         Assignor further represents and warrants that it has not granted any
rights inconsistent with the rights granted herein.

                                           SDR METRO INC.



                                           By
                                              --------------------------------



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


 State of                      )
          --------------------

                                  )SS

 County of                     )
          --------------------

         On this     day of                          ,200 , before me personally
                 ---        ------------------------

appeared                         , to me known to be the person named in and who
         -----------------------
executed the above instrument and acknowledged that he executed the same for the
uses and purposes therein mentioned.


                                               Notary Public



(SEAL)

<PAGE>


           UNANIMOUS JOINT WRITTEN CONSENT OF THE BOARD OF DIRECTORS
                      AND STOCKHOLDERS OF SDR METRO INC.

         The undersigned, as all of the members of the Board of Directors of
SDR METRO INC., ("Company") and all of the shareholders thereof, hereby jointly
consent to the following resolutions:

         WHEREAS, Company and RadioMetrix Incorporated (i.e. - Radio Metrix
Inc., a Florida corporation ["RadioMetrix"]), entered into a License Agreement
as of the 14th day of March 1992, and an Amendment thereto dated by the
parties on February 14, 1997 and May 26, 1998 respectively (collectively
hereinafter referred to as the "License Agreement").

         WHEREAS, Company, Brent Simon and RadioMetrix, Inc. entered into a
Purchase Agreement dated October 9, 2000 as extended by that certain Extension
Agreement entered into by and among the same parties on September 25, 2001
pursuant to which the Secured Party and Brent Simon agreed to sell to
RadioMetrix U.S. Patent No. 5,337,039 ("Patent") (collectively hereinafter
referred to as the "Purchase Agreement");

         WHEREAS, as part of the closing of the Purchase Agreement, the Board
of Directors of and stockholders of SDR METRO INC. wish to authorize, ratify,
approve and confirm the matters set forth below; be it then

         RESOLVED, and this confirms that the License Agreement and the
Company's assignment of same to RadioMetrix is hereby ratified, authorized and
approved.

         RESOLVED, and this confirms that the Purchase Agreement and the
closing of the Purchase Agreement are hereby ratified, authorized and approved;
and

         RESOLVED, and this confirms that the undersigned shareholders waive
any and all dissenter's rights under Ohio law and specifically hereby confirm
they will not be asserting any dissenter's rights with regard to the sale of
the Patent pursuant to the Purchase Agreement and the closing thereof.

         RESOLVED, that the following closing documents to the Purchase
Agreement are authorized, ratified and approved, and the Company's officers
are authorized and instructed to execute and deliver them, and any other
documents necessary to effectuate the resolutions set forth hereinabove:
Assignment of License Agreement, revised Promissory Note, Security Agreement,
Remedy Upon Default Agreement, Assignment, and Closing Agreement; and

         RESOLVED, and this confirms that the correct name of the corporation
is SDR METRO INC. and that while due to a typographical error SDR METRO INC.
was shown as SDR METRO INCORPORATED as a party to the Purchase Agreement and
License Agreement, SDR METRO INC. is the party to those agreements and each of
said contracts is hereby ratified in full.

DATE: January 8, 2002

DIRECTORS                              STOCKHOLDERS



      /s/ Roger Keith                          /s/ Roger Keith
--------------------------------       --------------------------------


          Roger Keith                              Roger Keith
--------------------------------       --------------------------------



--------------------------------       --------------------------------



--------------------------------       --------------------------------


<PAGE>

                                   ASSIGNMENT

         WHEREAS, SDR Metro Inc., a corporation of the State of Ohio, having
its principal place of business at 27367 Tungsten Road, Euclid, Ohio 44132,
hereinafter called Assignor, has title to the United States Patent Number
5,337,039.

         WHEREAS, Radio Metrix Inc., a corporation of the State of Florida
having its principal place of business at 4400 Independence Court, Sarasota,
Florida 34234, desires to acquire the entire right, title and interest in and
to said patent.

         NOW, THEREFORE, for and in consideration of the sum of One Dollar
($1.00) and other good and valuable considerations, receipt whereof is hereby
acknowledged, Assignor by these presents does sell, assign and transfer unto
said Assignee, its successors and assigns, all right, title and interest in the
United States of America to said patent, including all extensions, reissue
patents, and corresponding foreign equivalents and all inventions covered by
said patent.

         Assignor hereby agrees to execute any and all papers, including
further assignment documents of any and all kinds in any and all countries, and
to perform any and all acts which assignee may deem necessary to secure thereto
the rights herein assigned, sold and set over.


                                   EXHIBIT B

<PAGE>


         Assignor further represents and warrants that it has not granted any
rights inconsistent with the rights granted herein.


                                           SDR METRO INC.



                                           By
                                              --------------------------------



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


 State of                      )
          --------------------

                                  )SS

 County of                     )
          --------------------

         On this ___ day of ________________________, 200_, before me personally
appeared _______________________, to me known to be the person named in and who
executed the above instrument and acknowledged that he executed the same for the
uses and purposes therein mentioned.


                                               Notary Public



(SEAL)


<PAGE>


                                      Note

$600,000                                    Euclid, Ohio
                                                         ----------------------
                                                                (Date)

Radio Metrix Inc., after date for value received, promises to pay SDR Metro
Inc., an Ohio corporation, the sum of Six Hundred Thousand Dollars ($600,000),
with interest at the rate of eight per cent (8%) per annum, payable quarterly,
with principal due in one installment at the end of the twenty-fourth (24th)
month from the date hereof;

AND SUBJECT TO: (I) COMPLIANCE BY SDR METRO INC. AND BRENT SIMON, WITH THE
TERMS AND CONDITIONS OF THE AGREEMENT ENTERED INTO BY AND BETWEEN THEM AND
RADIO METRIX INC. ON OCTOBER 9, 2000; AND (II) WRITTEN NOTICE OF DEFAULT OF
THIS NOTE, PROVIDED BY CERTIFIED MAIL, RETURN RECEIPT REQUESTED, SENT TO
STEPHEN A. MICHAEL, PRESIDENT, 4400 INDEPENDENCE COURT, SARASOTA, FLORIDA 34234
AND SEPARATELY BY CERTIFIED MAIL, RETURN RECEIPT REQUESTED, TO SAMUEL S.
DUFFEY, CHAIRMAN, 4400 INDEPENDENCE COURT, SARASOTA, FLORIDA 34234, PROVIDING
NOTICE OF DEFAULT AND TEN (10) CALENDAR DAYS WITHIN WHICH RADIO METRIX INC. MAY
CURE SAID DEFAULT, RADIO METRIX INC. DOES HEREBY AUTHORIZE ANY ATTORNEY AT LAW
TO APPEAR FOR RADIO METRIX INC. IN AN ACTION ON THE ABOVE NOTE, AT ANY TIME
AFTER SAID NOTE BECOMES DUE, IN ANY COURT OF RECORD SITUATED IN THE COUNTY
WHERE RADIO METRIX INC. THEN RESIDES OR IN THE COUNTY WHERE RADIO METRIX INC.
SIGNED THIS WARRANT AND BEING IN THE UNITED STATES, TO WAIVE THE ISSUING AND
SERVICE OF PROCESS, AND CONFESS A JUDGMENT IN FAVOR OF THE LEGAL HOLDER OF THE
ABOVE AGAINST RADIO METRIX INC., FOR THE AMOUNT THAT MAY THEN BE DUE THEREON,
WITH INTEREST AT THE RATE THEREIN MENTIONED, AND COSTS OF SUIT, AND TO WAIVE
AND RELEASE ALL ERRORS IN SAID PROCEEDINGS AND THE RIGHT OF APPEAL FROM THE
JUDGMENT RENDERED.

WARNING: BY SIGNING THIS PAPER YOU GIVE UP YOUR RIGHT TO NOTICE AND COURT
TRIAL. IF YOU DO NOT PAY ON TIME A COURT JUDGMENT MAY BE TAKEN AGAINST YOU
WITHOUT YOUR PRIOR KNOWLEDGE AND THE POWERS OF A COURT CAN BE USED TO COLLECT
FROM YOU OR YOUR EMPLOYER REGARDLESS OF ANY CLAIMS YOU MAY HAVE AGAINST THE
CREDITOR WHETHER FOR RETURNED GOODS, FAULTY GOODS, FAILURE ON ITS PART TO
COMPLY WITH THE AGREEMENT OR ANY OTHER CAUSE.

                                             Radio Metrix Inc.



                                      By:
                                          ------------------------------------
                                           Stephen A. Michael, Its: President

         The rights of the parties hereunder shall, in the event of default
hereof, be governed by the Remedy upon Default Agreement executed on even date
by SDR Metro Inc. and Radio Metrix Inc.



 Radio Metrix Inc.                           SDR Metro Inc.



 By:                                         By:
     -------------------------------            -------------------------------
         Stephen A. Michael
 As Its:                                     As Its:


                                   EXHIBIT C


<PAGE>



                                                           RADIO METRIX, INC.

MEMO

To:           Brent Simon, SDR Metro, Inc.         via: fax
From:         S. A. Michael, President                     --------------------
CC:           SSD, file                                    --------------------
Date:         8/28/00
Re:           Consulting Agreement

                   ------------------------------------------

Brent,

Your continued involvement in the development of technologies attractive to
Radio Metrix, Inc. can only be positive. Because we believe this to be true we
have decided to accept your offer of consultation to Radio Metrix, Inc. Your
experience and creativity should be a productive addition to the R & D process.
This decision is important and will hopefully lead to a deeper involvement as
successful development projects follow.

Our legal department will (simultaneously with the execution of the patent
purchase agreement) prepare a consulting agreement, which will set forth our
mutual understanding. The following are some of the points to which we have
tentatively agreed:

1.       All developments and inventions which are covered by or which
         constitute a continuation, improvement, expansion or incorporation of
         Patent No. 5,337,039 will be the exclusive property of Radio Metrix,
         Inc. You will execute any assignments, reasonably requested by Radio
         Metrix, Inc. to reflect its ownership.

2.       As your availability permits, you will provide problem solving and
         development engineering services to Radio Metrix, Inc., based on tasks
         requested by Radio Metrix, Inc. which are intended to support the
         ongoing R & D of the technology described in Paragraph 1 above. For
         such tasks, you will be paid out-of-pocket expense reimbursements
         immediately upon the submission of two working prototypes, complete
         schematics and drawings, and a materials list of the task assigned
         together with appropriate receipts. Any expense in excess of $500.00
         will require pre-approval in writing from Radio Metrix, Inc.
         Approved expenses will be limited to hardware, components, assembly
         materials and other verifiable non-time, non-space and non-travel
         expenses necessary to complete the tasks assigned by Radio Metrix,
         Inc. and accepted by you. All products of such assigned tasks will be
         the property of Radio Metrix, Inc.

3        Should you identify additional projects or tasks which are outside of
         the material covered in Paragraph 1 hereof, and which are free to be
         controlled by mutual confidentiality agreements between the parties,
         you will submit same in detailed writing to Radio Metrix, Inc. for
         concept review. Should Radio Metrix, Inc., upon completion of review,
         accept the responsibility to fund "first stage" confidential
         development of your concept, you will then be authorized in writing to
         pursue the development and to submit prototypes exclusively to Radio
         Metrix, Inc. for viability review. In such instances, upon the
         submission of the prototypes, complete schematics and drawings,
         material lists, and appropriate receipts, you will be reimbursed for
         out-of-pocket expenses. Any out-of-pocket expense in excess of $500.00
         will require advanced written approval. Should Radio Metrix, Inc.
         determine, in the exercise of its discretion to proceed with ongoing
         development or commercialization of the developments or inventions
         developed under this Paragraph, the parties will execute a written
         agreement setting forth ownership of the technology/invention, future
         compensation if the technology is commercialized, and specific
         authorization and funding/expense reimbursement agreements regarding
         further stages of development.


                                   EXHIBIT D