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                                                                     EXHIBIT 4.1

                               REPLACEMENT OPTION

                                 SMARTGATE, INC.

       This certifies that, H.R. Williams Family Limited Partnership (the
Holder") is entitled at any time until December 31, 2001 to purchase and
receive 446,804 Shares of SmartGate, Inc., a Nevada corporation (the "Company"
or "SmartGate") capital stock. The exercise price under this Option shall be
$1.0657716 per share. In the event that SmartGate issues any Options from the
date hereof and during the Term of this Option at a price less than $1.0657716
per share then the Option exercise price hereunder shall be automatically
reduced to the lowest price reflected in any such option. This Option may be
accelerated by the Company during the calendar year 2001 provided that the
exercise price is discounted at the rate of 1% of the purchase price for each
month accelerated.

       This Option and the shares that may be acquired under this Option may be
assigned by the Holder and Holder in whole or in part to any family member or
any trust or other entity created by the Holder for the benefit of his family
members. Further, this Option may be exercised by the Holder in part and any
remaining unexercised portion of the Option shall remain intact and be
exercisable for the balance of the Term of this Option.

       SHARES ISSUED UPON THE EXERCISE OF THIS OPTION WILL BE RESTRICTED IN
ACCORDANCE WITH APPLICABLE STATE AND FEDERAL SECURITIES LAWS.

       In the event of a stock dividend or stock split resulting in the number
of outstanding of shares of the Company being changed, the applicable exercise
price and number of shares, as provided in this Option, shall be proportionately
adjusted. In the event of the merger, consolidation, or combination of the
Company into another company or entity which survives that transaction, the
shares which may be purchased under this Option shall be converted into an
equivalent number of shares of the surviving entity. In the event of the sale of
all or substantially all of the assets of the Company, the shares which may be
purchased upon the exercise of the Option shall be treated in any distribution
as if said shares are issued and outstanding, with the exception that the
exercise price under this Option shall be deducted from the amount to be
distributed on a per-share basis.

       This Option shall not entitle the Holder to voting or other rights of a
shareholder or to any dividends declared upon shares unless the holder shall
have exercised the Option and purchased the shares prior to the record date
fixed by the Company for such action.

       This Option is being issued by SmartGate, Inc., in exchange and
replacement for an Option representing 476,191 shares of SmartGate, L.C. (the
"Surrendered Option"). The Surrendered Option was issued by SmartGate, L.C., a
Florida limited liability company. The Surrendered Option shall be rendered void
and unenforceable by virtue of the acceptance by Holder of this Replacement
Option issued by SmartGate, Inc.

       IN WITNESS WHEREOF, the Company has caused this Option to be signed and
sealed by its duly authorized officer.

                                                      SmartGate, Inc.
                                                      a Nevada corporation

Dated: As of 2-9-2000                          By: /s/ STEPHEN A. MICHAEL
       --------------                              -----------------------------
                                                   Stephen A. Michael, President

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                       AMENDMENT TO SUBSCRIPTION AGREEMENT

       This Amendment to Subscription Agreement is entered into April 27, 2001
by and among H.R. Williams Family Limited Partnership ("Partnership"), H.R.
Williams, SmartGate, L.C. ("SmartGate") and SmartGate, Inc. to amend that
certain Subscription Agreement (the "Subscription Agreement") between the
Partnership and SmartGate dated March 1, 1999.

       WHEREAS, pursuant to the Subscription Agreement, the Partnership was
granted an option to purchase 476,191 shares of SmartGate, L.C. at $1.00 per
share with an exercise period to terminate on December 31, 2001 ("Option"); and

       WHEREAS, pursuant to the Contribution Agreement entered into by and among
the Partnership, as a member of SmartGate, SmartGate, and SmartGate, Inc. dated
February 9, 2000, the Partnership's Option was converted into an option to
purchase an equivalent number of SmartGate, Inc. shares in accordance with the
conversion ratio utilized under the Conversion Agreement for the exchange of
SmartGate, L.C. shares to SmartGate, Inc. shares ("Replacement Option"), a copy
of which is attached hereto; and

       WHEREAS, the Replacement Option issued to the Partnership is for the
purchase of 446,804 shares of SmartGate, Inc. at $1.0657716 per share with an
exercise period to terminate on December 31, 2001; and

       WHEREAS, pursuant to the Subscription Agreement, H.R. Williams agreed to
personally guarantee a credit facility for SmartGate and that said guarantee
would remain in effect for a period of twenty-four (24) months; and

       WHEREAS, the parties wish to extend the period of the personal guarantee
and the exercise period of the Replacement Option by amending the Subscription
Agreement as set forth hereinbelow.

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

       1. REPLACEMENT OPTION EXERCISE PERIOD EXTENSION. The reference to the
Option in Paragraph 2(a) of the Subscription Agreement is hereby amended to
reference the Replacement Option, and the exercise period of the Replacement
Option is amended as follows: the exercise period termination date of December
31, 2001 is hereby cancelled and deleted. The termination date for the exercise
period under the Replacement Option is hereby extended to be the 245th day
following the first date upon which either: (i) SmartGate's line of credit
facility with Regions Bank ("Credit Facility") or a replacement bank if Regions
Bank is unwilling to extend said credit facility ("Replacement Credit Facility")
is paid off; or (ii) H.R. Williams' guarantee is released by SmartGate from the
Credit Facility or the Replacement Credit Facility (the "Option Release
Conditions"). Upon satisfaction of the Option Release Conditions, SmartGate will
advise the Partnership that the Option Release Conditions has been satisfied and
that the period to exercise the Replacement Option will terminate on the 245th
day following said date ("New Exercise Termination Date"). The parties further
agree that all other terms of the Replacement Option remain in full force and
effect and that this Amendment shall serve as the amendment to the Replacement
Option establishing the New Exercise Termination Date.

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       2. CREDIT FACILITY GUARANTY EXTENSION. Mr. Williams shall renew and
extend his guarantee of SmartGate's line of credit facility with Regions Bank
(or a Replacement Credit Facility) for an additional two-year period.
Accordingly, Paragraph 2(b)(iii) of the Subscription Agreement is hereby amended
to reflect this guarantee extension.

       3. REMAINDER OF SUBSCRIPTION AGREEMENT BINDING. Except as herein
modified, the Subscription Agreement and the Replacement Option and all of the
terms and conditions therein shall remain unmodified and in full force and
effect.

       4. COUNTERPARTS. This Amendment to Subscription Agreement may be executed
in several counterparts, each of which shall be fully effective as an original,
and all of which together shall constitute one in the same instrument. A
facsimile copy of this Agreement and counterpart signature shall be considered,
for all purposes, as an original.

       IN WITNESS WHEREOF, the undersigned have caused the execution of this
Amendment to Subscription Agreement by them on April 27, 2001.

H.R. Williams Family Limited Partnership         SmartGate, L.C.

By: /s/ H.R. WILLIAMS                      By: /s/ STEPHEN A. MICHAEL, PRESIDENT
    -----------------                          ---------------------------------

H.R. Williams                                   SmartGate, Inc.

    /s/ H.R. WILLIAMS                      By: /s/ STEPHEN A. MICHAEL, PRESIDENT
    -----------------                          ---------------------------------
H.R. Williams<PAGE>
                                                                     EXHIBIT 4.2

                               REPLACEMENT OPTION
                                  INVISA, INC.

        This certifies that William Hyde (the "Holder") is entitled at any time
until December 31, 2000 and before December 31, 2002 to purchase and receive
14,074 shares of Invisa, Inc. (the "Company" or "Invisa") capital stock. The
exercise price under this Option shall be $1.0657951 per share.

        This Option and the shares that may be acquired under this Option may be
assigned by the Holder. Further, this Option may be exercised by the Holder in
part and any remaining unexercised portion of the Option shall remain intact and
be exercisable for the balance of the Term of this Option.

        SHARES ISSUED UPON THE EXERCISE OF THIS OPTION WILL BE RESTRICTED IN
ACCORDANCE WITH APPLICABLE STATE AND FEDERAL SECURITIES LAWS.

        This Option shall not entitle the Holder to voting or other rights of a
shareholder or to any dividends declared upon shares unless the Holder shall
have exercised the Option and purchased the shares prior to the record date
fixed by the Company for such action.

        This Option is being issued by Invisa, Inc. in exchange and replacement
for an Option representing 15,000 shares of SmartGate, L.C. (the "Surrendered
Option"). The Surrendered Option was issued by SmartGate, L.C., a Florida
limited liability company. The Surrendered Option shall be rendered void and
unenforceable by virtue of the acceptance by Holder of this Replacement Option
issued by Invisa, Inc.

        IN WITNESS WHEREOF, the Company has caused this Option to be signed and
sealed by its duly authorized officer.

Dated: May 8, 2002                              Invisa, Inc.

                                                By: /s/ SAMUEL S. DUFFEY
                                                    --------------------------
                                                    Samuel S. Duffey, Chairman

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