<PAGE>

                                                                     EXHIBIT 4.1


                             VICOM INCORPORATED

                          CERTIFICATE OF DESIGNATION
                                    OF THE
                 RELATIVE RIGHTS, RESTRICTIONS AND PREFERENCES
                                      OF
               8% CLASS A CUMULATIVE CONVERTIBLE PREFERRED STOCK
                                      AND
              10% CLASS B CUMULATIVE CONVERTIBLE PREFERRED STOCK

    Pursuant to Section 302A.401 of the Minnesota Business Corporations Act

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

     The undersigned, as the Chief Executive Officer of Vicom Incorporated, a
Minnesota corporation (the "Corporation"), hereby certifies that on the 9th
day of December, 1998, the following resolutions were adopted by the Board of
Directors of the Corporation for the purpose of designating a portion of the
Corporation's authorized but unissued capital stock as Preferred Stock and
establishing two classes of Preferred Stock designated as "8% Class A
Cumulative Convertible Preferred Stock" and "10% Class B Cumulative
Convertible Preferred Stock":

     "RESOLVED, that pursuant to authority granted to and vested in the Board
     of Directors by the laws of the State of Minnesota and the Corporation's
     Articles of Incorporation, as amended and restated, the Board of Directors
     hereby establishes the following classes of capital stock:

     A.   Two Hundred Seventy-five Thousand (275,000) shares of the
          Corporation's authorized but unissued capital stock shall be Preferred
          Stock, with no par value per share, designated as "8% Class A
          Cumulative Convertible Preferred Stock";

     B.   Sixty Thousand (60,000) shares of the Corporation's authorized but
          unissued capital stock shall be Preferred Stock, with no par value
          per share, designated as "10% Class B Cumulative Convertible
          Preferred Stock"; and

     C.   The remaining balance of the Corporation's authorized but unissued
          capital stock shall be undesignated as to class or series.

     FURTHER RESOLVED, that the 8% Class A Cumulative Convertible Preferred
     Stock and the 10% Class B Cumulative Convertible Preferred Stock shall
     have the relative rights, restrictions and preferences set forth in
     APPENDIX A attached hereto."

     IN WITNESS WHEREOF, I have hereunder subscribed my name this 9th day of
     December, 1998.

                                            /s/ James L. Mandel
                                            ----------------------------------
                                            James L. Mandel
                                            Chief Executive Officer

<PAGE>

                                                                      APPENDIX A


                              VICOM INCORPORATED

               8% CLASS A CUMULATIVE CONVERTIBLE PREFERRED STOCK
                                      AND
              10% CLASS B CUMULATIVE CONVERTIBLE PREFERRED STOCK

     The total number of shares of all classes of capital stock which the
Corporation is authorized to issue is Fifty Million (50,000,000). The shares
of capital stock of the Corporation shall include a class of preferred stock
consisting of Two Hundred Seventy-five Thousand (275,000) shares, which shall
be designated 8% Class A Cumulative Convertible Preferred Stock with no par
value per share ("Class A Preferred"), and a second class of preferred stock
consisting of Sixty Thousand (60,000) shares, which shall be designated 10%
Class B Cumulative Convertible Preferred Stock with no par value per share
("Class B Preferred"). The balance of the Corporation's authorized but
unissued capital stock shall be undesignated capital stock. The rights,
preferences, privileges, restrictions and other matters relating to the Class
A Preferred Stock and Class B Preferred Stock are as follows:

     1.  DIVIDENDS.  Holders of the Class A Preferred and Class B Preferred
shall be entitled to receive, when and as declared by the Board of Directors
out of funds legally available therefor, cumulative cash dividends at the
rates set forth below in paragraphs 1A and 1B, respectively. For purposes of
calculating the dividends payable on the Class A Preferred and Class B
Preferred, each share of Class A Preferred and Class B Preferred shall be
valued at $10.00 per share (appropriately adjusted for stock dividends, stock
splits, reverse stock splits, and other subdivisions and combinations of
Class A Preferred and Class B Preferred) (such per share price, as it may be
adjusted, for the Class A Preferred and Class B Preferred is referred to
herein as the "Dividend Price"). All dividends payable pursuant to this
Section 1 shall be referred to as "Preferred Dividends."

         A.  CLASS A PREFERRED.  The holders of shares of Class A Preferred
     shall be entitled to receive, when and as declared by the Board of
     Directors of the Corporation out of assets of the Corporation legally
     available for payment thereof, cumulative cash dividends on the Dividend
     Price then in effect for the Class A Preferred at the per annum rate,
     computed on the basis of actual days over a 365-day year, of eight percent
     (8%) per annum. Such dividends shall be payable upon declaration quarterly
     on March 31, June 30, September 30 and December 31 of each year,
     commencing for any share of Class A Preferred on the first of such dates
     to occur after that share is issued.

         B.  CLASS B PREFERRED.  The holders of shares of Class B Preferred
     shall be entitled to receive, when and as declared by the Board of
     Directors of the Corporation out of assets of the Corporation legally
     available for payment thereof, cumulative cash dividends on the Dividend
     Price then effect for the Class B Preferred at the per annum rate,
     computed on the basis of actual days over a 365-day year, of ten percent
     (10%) per annum. Such dividends shall be payable upon declaration monthly
     on the first day of each calendar month, commencing for any share of
     Class B Preferred on the first day of a calendar month to occur after such
     share is issued.

         C.  ACCRUAL; PAYMENT.  The Preferred Dividends on the Class A
     Preferred and Class B Preferred shall accrue cumulatively on a daily basis
     from and as of the date of original issuance of the Class A Preferred and
     Class B Preferred until such time as the Class A Preferred and Class B
     Preferred are redeemed or converted, whether or not declared and whether
     or not any funds of the Corporation are legally available for the payment
     of dividends. Preferred Dividends shall be payable to holders of record of
     the Class A Preferred and Class B Preferred as they appear on the books of
     the Corporation on the record date determined by the Board of Directors.
     Preferred


                                       1

<PAGE>

     Dividends payable for the initial dividend period shall be based on the
     amount of dividends accrued since the date of issuance of the Class A
     Preferred and Class B Preferred.

     2.  DIVIDEND PRIORITIES.  No dividend payments shall be paid or declared
and set apart for payment on any other shares of stock of the Corporation,
whether common or preferred, for any period, and no other shares of the
Corporation, whether common or preferred, shall be redeemed or purchased by
the Corporation, unless all Preferred Dividends have been paid or
contemporaneously are declared and paid on the Class A Preferred and Class B
Preferred for such period. Except as provided in Section 1 above, holders of
the Class A Preferred and Class B Preferred shall not be entitled to any
dividends, whether payable in cash, property or stock, in excess of the full
Preferred Dividends for any period. No interest, or sum of money in lieu of
interest, shall be payable in respect of any Preferred Dividend payments or
payment which may be in arrears. If at any time the Corporation pays less
than the total amount of Preferred Dividends then accrued with respect to the
Class A Preferred and Class B Preferred, such payment shall be distributed
ratably among the holders of Class A Preferred and Class B Preferred based
upon the aggregate accrued but unpaid dividends on the shares of Class A
Preferred and Class B Preferred held by each such holder on the record date
fixed by the Board of Directors for the payment of such dividend. The Board
of Directors, in its discretion, may declare and pay dividends on the common
stock or other capital stock of the Corporation, provided that all accumulated
Preferred Dividends on the Class A Preferred and Class B Preferred for the
current and all previous dividend periods have been paid in full. In the
event that, for a given year, the dividends declared on the common stock of
the Corporation exceed, on a per share basis, the year to date per share
Preferred Dividends accrued, declared and paid on the Class A Preferred and
Class B Preferred, the Class A Preferred and Class B Preferred shall
participate in and shall receive a pro rata share of the excess amount. Such
allocation shall be adjusted as appropriate to account for any change in the
capitalization of the Corporation occurring after the date hereof, whether
resulting from a recapitalization, stock dividend, stock split, reverse stock
split or otherwise.

     3.  LIQUIDATION PREFERENCES.

         A.  Upon any liquidation, dissolution or winding up of the Corporation,
     whether voluntary or involuntary, the holders of the shares of Class A
     Preferred and Class B Preferred shall be entitled, after payment or
     provision for all debts and liabilities of the Corporation and before any
     distribution or payment is made upon any other shares of capital stock of
     the Corporation, to be paid an amount per share equal to the sum of
     (i) $10.50 per share (appropriately adjusted for stock dividends, stock
     splits, reverse stock splits, and other subdivisions and combinations of
     Class A Preferred and Class B Preferred) (such per share price, as
     adjusted, for the Class A Preferred and Class B Preferred is referred to
     herein as the "Preferred Price") plus (ii) accrued and unpaid Preferred
     Dividends due under Section 1 above. (Such total sum of the amounts
     payable referred to in clauses (i) and (ii) being sometimes referred to
     herein as the "Preferential Amount.") If upon such liquidation, dissolution
     or winding up of the Corporation, whether voluntary or involuntary, the
     assets to be distributed among the holders of Class A Preferred and Class B
     Preferred shall be insufficient to permit payment to the holders of Class A
     Preferred and Class B Preferred of the amount distributable as aforesaid,
     then all of the assets of the Corporation remaining to be so distributed
     shall be distributed ratably (a) first among the holders of the shares of
     Class A Preferred and Class B Preferred so that the same percentage of the
     Preferred Price for each share of Class A Preferred and Class B Preferred
     is paid with respect to each such share, until the full amount of the
     Preferred Price has been paid; and (b) then among the holders of the shares
     of Class A Preferred and Class B Preferred so that the same percentage of
     the Preferred Dividends for each share of Class A Preferred and Class B
     Preferred is paid with respect to each such share, until the full amount of
     the Preferred Dividends has been paid.


                                       2

<PAGE>

          B.   Upon any such liquidation, dissolution or winding up of the
     Corporation, after the holders of Class A Preferred and Class B
     Preferred shall have been paid in full the amounts to which they shall be
     entitled, the remaining net assets of the Corporation may be distributed
     pro rata to the holders of shares of common stock of the Corporation;
     provided that in the event that, upon liquidation and dissolution of the
     Corporation, the amounts distributed to the holders of the shares of
     common stock of the Corporation exceed, on a per share basis, the amount
     of the Preferential Amount, the holders of the Class A Preferred and
     Class B Preferred shall participate in and shall receive a pro rata share
     of the excess.

          C.   Written notice of such liquidation, dissolution or winding up,
     stating a payment date, the amount of the Preferential Amount and the place
     where said Preferential Amount shall be payable, shall be delivered in
     person, mailed by certified or registered mail, return receipt requested,
     or sent by telecopier or telex, not less than twenty (20) business days
     prior to the payment date stated therein, to the holders of record of Class
     A Preferred and Class B Preferred, such notice to be addressed to each such
     holder at its address as shown by the records of the Corporation. The
     consolidation or merger of the Corporation into or with any other entity or
     entities which results in the exchange of outstanding shares of the
     Corporation for securities or other consideration issued or paid or caused
     to be issued or paid by any such entity or affiliate thereof, and the sale,
     lease, abandonment, transfer or other disposition by the Corporation of all
     or substantially all its assets, shall be deemed to be a liquidation,
     dissolution or winding up of the Corporation within the meaning of the
     provisions of this Section 3.

     4.   VOTING RIGHTS. The Class A Preferred and the Class B Preferred are
non-voting, except as may otherwise be required by law.

     5.   CONVERSIONS. The holders of shares of Class A Preferred and Class B
Preferred shall have the following conversion rights:

          A.   RIGHT TO CONVERT. Subject to the terms and conditions of this
     Section 5, the holder of any share or shares of Class A Preferred or Class
     B Preferred shall have the right, at his or her option at any time, to
     convert any such share or shares of Class A Preferred or Class B Preferred
     (except that upon any liquidation of the Corporation the right of
     conversion shall terminate at the close of business on the business day
     prior to the date fixed for payment of the amount distributable on Class A
     Preferred or Class B Preferred) into five (5) fully paid and nonassessable
     shares of the Corporation's common stock, no par value per share (the
     "Common Stock"), or, in case an adjustment has taken place pursuant to the
     further provisions of this Section 5, then by the conversion ratio as last
     adjusted and in effect at the date any share or shares of Class A Preferred
     or Class B Preferred are surrendered for conversion (such ratio, or such
     ratio as last adjusted, being referred to as the "Conversion Ratio"). Such
     rights of conversion shall be exercised by the holder thereof by giving
     written notice that the holder elects to convert a stated number of shares
     of Class A Preferred or Class B Preferred into Common Stock and by
     surrender of a certificate or certificates for the shares so to be
     converted to the Corporation at its principal office (or such other office
     or agency of the Corporation as the Corporation may designate by notice in
     writing to the holders of Class A Preferred and Class B Preferred) at any
     time during its usual business hours on the date set forth in such notice,
     together with a statement of the name or names (with address) in which the
     certificate or certificates for shares of Common Stock shall be issued.

          B.   ISSUANCE OF CERTIFICATES; TIME CONVERSION EFFECTED. Promptly
     after the receipt of the written notice referred to in paragraph 5A and
     surrender of the certificate or certificates for


                                       3
<PAGE>

     the share or shares of Class A Preferred or Class B Preferred to be
     converted, the Corporation shall issue and deliver, or cause to be issued
     and delivered, to the holder, registered in such name or names as such
     holder may direct, a certificate or certificates for the number of whole
     shares of Common Stock issuable upon the conversion of such share or shares
     of Class A Preferred or Class B Preferred. To the extent permitted by law,
     such conversion shall be deemed to have been effected and the Conversion
     Ratio shall be determined as of the close of business on the date on which
     such written notice shall have been received by the Corporation and the
     certificate or certificates for such share or shares shall have been
     surrendered as aforesaid, and at such time the rights of the holder of such
     share or shares of Class A Preferred or Class B Preferred shall cease, and
     the person or persons in whose name or names any certificate or
     certificates for shares of Common Stock shall be issuable upon such
     conversion shall be deemed to have become the holder or holders of record
     of the shares represented thereby.

          C.   FRACTIONAL SHARES: DIVIDENDS; PARTIAL CONVERSION. No fractional
     shares shall be issued upon conversion of Class A Preferred or Class B
     Preferred into Common Stock and no payment or adjustment shall be made upon
     any conversion on account of any cash dividends on the Common Stock issued
     upon such conversion. At the time of each conversion, the Corporation shall
     pay in cash an amount equal to all dividends declared pursuant to Section 1
     above and unpaid on the shares of Class A Preferred or Class B Preferred
     surrendered for conversion to the date upon which such conversion is deemed
     to take place as provided in paragraph 5B. In case the number of shares of
     Class A Preferred or Class B Preferred represented by the certificate or
     certificates surrendered pursuant to subparagraph 5A exceeds the number of
     shares converted, the Corporation shall, upon such conversion, execute and
     deliver to the holder, at the expense of the Corporation, a new certificate
     or certificates for the number of shares of Class A Preferred or Class B
     Preferred represented by the certificate or certificates surrendered which
     are not to be converted. If any fractional share of Common Stock would,
     except for the provisions of the first sentence of this paragraph 5C, be
     delivered upon such conversion, the Corporation, in lieu of delivering such
     fractional share, shall pay to the holder surrendering Class A Preferred or
     Class B Preferred for conversion an amount in cash equal to the current
     market price of such fractional share as determined in good faith by the
     Board of Directors of the Corporation.

          D.   STOCK DIVIDENDS, SUBDIVISION OR COMBINATION OF COMMON STOCK.  In
     case the Corporation shall, after the date on which the Class A Preferred
     and Class B Preferred are first issued by the Corporation (the "Original
     Issue Date"), at any time subdivide (by any stock split, stock dividend or
     otherwise) its outstanding shares of Common Stock into a greater number of
     shares, the Conversion Ratio in effect immediately prior to such
     subdivision shall be proportionately increased, and, conversely, in case
     the outstanding shares of Common Stock shall be combined into a smaller
     number of shares, the Conversion Ratio in effect immediately prior to such
     combination shall be proportionately reduced.

          E.   REORGANIZATION OR RECLASSIFICATION. If any capital reorganization
     or reclassification of the capital stock of the Corporation shall be
     effected after the Original Issue Date in such a way that holders of Common
     Stock shall be entitled to receive stock, securities or assets with respect
     to or in exchange for Common Stock, then, as a condition of such
     reorganization or reclassification, lawful and adequate provisions shall
     be made whereby each holder of a share or shares of Class A Preferred or
     Class B Preferred shall thereupon have the right to receive, upon the basis
     and upon the terms and conditions specified herein and in lieu of the
     shares of Common Stock immediately theretofore receivable upon the
     conversion of such share or shares of Class A Preferred or Class B
     Preferred, such shares of stock, securities or assets as may be issued or
     payable with respect to or in exchange for a number of outstanding shares
     of such Common Stock equal to the number of shares of such Common Stock
     immediately


                                       4
<PAGE>

     theretofore receivable upon such conversion had such reorganization or
     reclassification not taken place, and in any such case appropriate
     provisions shall be made with respect to the rights and interests of
     such holder to the end that the provisions hereof (including, without
     limitation, provisions for adjustments of the Conversion Ratio) shall
     thereafter be applicable, as nearly as may be, in relation to any shares
     of stock, securities or assets thereafter deliverable upon the exercise
     of such conversion rights.

          F.   NOTICE OF ADJUSTMENT.  Upon any adjustment of the Conversion
     Ratio, then and in each such case the Corporation shall give written notice
     thereof, by delivery in person, certified or registered mail, return
     receipt requested, telecopier or telex, addressed to each holder of
     shares of Class A Preferred or Class B Preferred at the address of such
     holder as shown on the books of the Corporation, which notice shall
     state the Conversion Ratio resulting from such adjustment, setting forth
     in reasonable detail the method upon which such calculation is based.

          G.   OTHER NOTICES.  In case at any time:

               (1)  the Corporation shall declare any dividend upon its
          Common Stock payable in stock or make any other distribution to the
          holders of its Common Stock;

               (2)  the Corporation shall offer for subscription pro rata to
          the holders of its Common Stock any additional shares of stock of
          any class or other rights;

               (3)  there shall be any capital reorganization or
          reclassification of the capital stock of the Corporation, or a
          consolidation or merger of the Corporation with or into another
          entity or entities, or a sale, lease, abandonment, transfer or
          other disposition of all or substantially all its assets; or

               (4)  there shall be a voluntary or involuntary dissolution,
          liquidation or winding up of the Corporation;

     then, in any one or more of said cases, the Corporation shall give, by
     delivery in person, certified or registered mail, return receipt
     requested, telecopier or telex, addressed to each holder of any shares of
     Class A Preferred or Class B Preferred at the address of such holder as
     shown on the books of the Corporation, (a) at least 20 days' prior
     written notice of the date on which the books of the Corporation shall
     close or a record shall be taken for such dividend, distribution or
     subscription rights or for determining rights to vote in respect of any
     such reorganization, reclassification, consolidation, merger,
     disposition, dissolution, liquidation or winding up and (b) in the case
     of any such reorganization, reclassification, consolidation, merger,
     disposition, dissolution, liquidation or winding up, at least 20 days'
     prior written notice of the date when the same shall take place. Such
     notice in accordance with the foregoing clause (a) shall also specify, in
     the case of any such dividend, distribution or subscription rights, the
     date on which the holders of Common Stock shall be entitled thereto and
     such notice in accordance with the foregoing clause (b) shall also
     specify the date on which the holders of Common Stock shall be entitled
     to exchange their Common Stock for securities or other property
     deliverable upon such reorganization, reclassification, consolidation,
     merger, disposition, dissolution, liquidation or winding up, as the case
     may be.

          H.   STOCK TO BE RESERVED.  The Corporation will at all times
     reserve and keep available out of its authorized Common Stock, solely
     for the purpose of issuance upon the conversion of Class A Preferred and
     Class B Preferred as herein provided, such number of shares of Common
     Stock as shall then be issuable upon the conversion of all outstanding
     shares of Class


                                       5

<PAGE>

     A Preferred and Class B Preferred.  The Corporation covenants that all
     shares of Common Stock which shall be so issued shall be duly and
     validly issued and fully paid and nonassessable and free from all
     transfer taxes, liens and charges with respect to the issue thereof.
     The Corporation will take all such action as may be necessary to assure
     that all such shares of Common Stock may be so issued without violation
     of any applicable law or regulation, or of any requirement of any
     national securities exchange upon which the Common Stock may be listed.

          I.  NO REISSUANCE OF CLASS A PREFERRED AND CLASS B PREFERRED.
     Shares of Class A Preferred and Class B Preferred which are converted
     into shares of Common Stock as provided herein shall not be reissued.

          J.  ISSUE TAX.  The issuance of certificates for shares of Common
     Stock upon conversion of Class A Preferred and Class B Preferred shall
     be made without charge to the holders thereof for any issuance tax in
     respect thereof, provided that the Corporation shall not be required to
     pay any tax which may be payable in respect of any transfer involved in
     the issuance and delivery of any certificate in a name other than that
     of the holder of Class A Preferred and Class B Preferred which is being
     converted.

          K.  CLOSING OF BOOKS.  Except as required by an underwriter in
     connection with a public offering, the Corporation will at no time close
     its transfer books against the transfer of any Class A Preferred or
     Class B Preferred or of any shares of Common Stock issued or issuable
     upon the conversion of any shares of Class A Preferred or Class B
     Preferred in any manner which interferes with the timely conversion of
     such Class A Preferred and Class B Preferred, except as may otherwise be
     required to comply with applicable securities laws.

     6.   REDEMPTION.  The Corporation shall have the right to redeem the
outstanding shares of Class A Preferred and Class B Preferred, in whole or in
part, at a redemption price of $10.50 per share (appropriately adjusted for
stock dividends, stock splits, reverse stock splits, and other subdivisions
and combinations of Class A Preferred or Class B Preferred) plus any earned
and unpaid Preferred Dividends, or not less than thirty (30) calendar days'
notice ("Corporate Notice") to the holders of the Class A Preferred or Class
B Preferred.  The Corporation shall be entitled to redeem the Class A
Preferred and the Class B Preferred as provided in this Paragraph 6 only if
the closing bid price of the Common Stock exceeds $4.00 per share
(appropriately adjusted for stock dividends, stock splits, reverse stock
splits and other subdivisions and combinations of Common Stock) for any ten
(10) consecutive trading days prior to the date of the Corporate Notice.
Upon receipt of Corporate Notice, the holders of the Class A Preferred and
Class B Preferred to be redeemed will have the option to convert each share
of Class A Preferred and Class B Preferred into five (5) shares of Common Stock
(subject to adjustment as set forth in Section 5 above) until the close of
business on the date fixed for redemption, unless extended by the Corporation
in its sole discretion.  All shares of Class A Preferred and Class B
Preferred called for redemption which are not so converted will be redeemed.
Each holder of shares of Class A Preferred and Class B Preferred to be
redeemed shall surrender the certificate or certificates representing such
shares to the Corporation at the place designated in the Corporate Notice,
and thereupon the applicable redemption price for such shares as set forth in
this Section 6 shall be paid to the order of the person whose name appears on
such certificate or certificates and each surrendered certificate shall be
canceled and retired.  Holders of Class A Preferred and Class B Preferred
shall not have the right to require the Corporation to redeem their shares of
Class A Preferred or Class B Preferred.


                                                                          [SEAL]


                                       6