<PAGE>

                                                                     EXHIBIT 4.2

                          TYCO INTERNATIONAL GROUP S.A.

                             TYCO INTERNATIONAL LTD.

                          SUPPLEMENTAL INDENTURE NO. 15

                                 $1,000,000,000

                              6.375% Notes due 2006


      THIS SUPPLEMENTAL INDENTURE NO. 15, dated as of February 21, 2001, among
TYCO INTERNATIONAL GROUP S.A., a Luxembourg company (the "COMPANY"), TYCO
INTERNATIONAL LTD., a Bermuda company ("TYCO"), and THE BANK OF NEW YORK, a New
York banking corporation, as trustee (the "TRUSTEE").

                              W I T N E S S E T H:
                               - - - - - - - - - -

      WHEREAS, the Company and Tyco have heretofore executed and delivered to
the Trustee an Indenture, dated as of June 9, 1998 (the "INDENTURE"), providing
for the issuance from time to time of one or more series of the Company's
Securities;

      WHEREAS, Article Seven of the Indenture provides for various matters with
respect to any series of Securities issued under the Indenture to be established
in an indenture supplemental to the Indenture; and

      WHEREAS, Section 7.1(e) of the Indenture provides that the Company, Tyco
and the Trustee may enter into an indenture supplemental to the Indenture to
establish the form or terms of Securities of any series as permitted by Sections
2.1 and 2.4 of the Indenture;

      NOW, THEREFORE, in consideration of the premises and the issuance of the
series of Securities provided for herein, the Company, Tyco and the Trustee
mutually covenant and agree for the equal and proportionate benefit of the
respective Holders of the Securities of such series as follows:

                                    ARTICLE 1

                       RELATION TO INDENTURE; DEFINITIONS

      SECTION 1.1. INTEGRAL PART. This Supplemental Indenture No. 15 constitutes
an integral part of the Indenture.


<PAGE>

      SECTION 1.2. GENERAL DEFINITIONS. For all purposes of this Supplemental
Indenture No. 15:

      (a) capitalized terms used herein without definition shall have the
meanings specified in the Indenture;

      (b) all references herein to Articles and Sections, unless otherwise
specified, refer to the corresponding Articles and Sections of this Supplemental
Indenture No. 15;

      (c) the terms "herein", "hereof", "hereunder" and other words of similar
import refer to this Supplemental Indenture No. 15; and

      (d) in the event of a conflict between any definition set forth in the
Indenture and any definition set forth in this Supplemental Indenture No. 15,
the definition set forth in this Supplemental Indenture No. 15 shall control.

      SECTION 1.3. DEFINITIONS. The following definitions shall apply to this
Supplemental Indenture No. 15:

      "ADJUSTED REDEMPTION TREASURY RATE" means, with respect to any redemption
date, the annual rate equal to the semiannual equivalent yield to maturity or
interpolated (on a 30/360 day count basis) yield to maturity of the Comparable
Redemption Treasury Issue, assuming a price for the Comparable Redemption
Treasury Issue (expressed as a percentage of its principal amount) equal to the
Comparable Redemption Treasury Price for such redemption date.

      "BUSINESS DAY" means any day other than a Saturday, a Sunday or a day on
which banking institutions in The City of New York are authorized or obligated
by law, executive order or governmental decree to be closed.

      "COMPARABLE REDEMPTION TREASURY ISSUE" means the United States Treasury
security selected by the Quotation Agent as having a maturity comparable to the
remaining term of the Notes to be redeemed that will be utilized at the time of
selection and in accordance with customary financial practice in pricing new
issues of corporate debt securities of comparable maturity to the remaining term
of such Notes.

      "COMPARABLE REDEMPTION TREASURY PRICE" means, with respect to any
redemption date, (i) the average of the Redemption Reference Treasury Dealer
Quotations for such redemption date, after excluding the highest and lowest such
Redemption Reference Treasury Dealer Quotations (unless there is more than one
highest or lowest quotation, in which case only one such highest and/or lowest
quotation shall be excluded), or (ii) if the Quotation Agent obtains fewer than
four such Redemption

                                       2

<PAGE>

Reference Treasury Dealer Quotations, the average of all such Redemption
Reference Treasury Dealer Quotations.

      "NOTES" means the 6.375% Notes due 2006 of the Company to which this
Supplemental Indenture No. 15 relates.

      "QUOTATION AGENT" means a Redemption Reference Treasury Dealer appointed
as such agent by the Company.

      "REDEMPTION REFERENCE TREASURY DEALER" means each of Banc of America
Securities LLC and Lehman Brothers Inc. and three other primary U.S. Government
securities dealers in The City of New York selected by the Company.

      "REDEMPTION REFERENCE TREASURY DEALER QUOTATIONS" means, with respect to
each Redemption Reference Treasury Dealer and any redemption date, the offer
price for the Comparable Redemption Treasury Issue (expressed in each case as a
percentage of its principal amount) for settlement on the redemption date quoted
in writing to the Quotation Agent by such Redemption Reference Treasury Dealer
at 5:00 p.m., New York City time, on the third Business Day preceding such
redemption date.


                                    ARTICLE 2

                               THE SERIES OF NOTES

      SECTION 2.1. TITLE OF THE SECURITIES. There shall be a series of
Securities designated as the "6.375% Notes due 2006" (the "NOTES").

      SECTION 2.2. LIMITATION ON AGGREGATE PRINCIPAL AMOUNT; DATE OF NOTES. The
aggregate principal amount of the Notes shall not initially exceed
$1,000,000,000 (unless the issue of such series of Notes is "reopened" pursuant
to Section 7.1(h) of the Indenture (as set forth herein) by issuing additional
Notes of such series, in an amount or amounts and registered in the names of
such Persons as shall be set forth in any written order of the Issuer for the
authentication and delivery of Notes pursuant to Section 2.5 of the Indenture).
Each Note shall be dated the date of its authentication.

      SECTION 2.3. PRINCIPAL PAYMENT DATE. Subject to the provisions of Section
2.6 hereof and Articles Four and Twelve of the Indenture, the principal of the
Notes shall be due and payable in a single installment on February 15, 2006.

                                       3

<PAGE>

      SECTION 2.4. INTEREST AND INTEREST RATES. Interest on the Notes shall be
payable semi-annually on February 15 and August 15 of each year beginning on
August 15, 2001 (each, an "INTEREST PAYMENT DATE"); provided, however, that if
an Interest Payment Date would otherwise be a day that is not a Business Day,
such Interest Payment Date shall be the next succeeding Business Day, and no
additional interest shall be paid in respect of such intervening period.

      The interest payable on each Interest Payment Date shall be the amount of
interest accrued from February 21, 2001 or from the most recent Interest Payment
Date to which interest has been paid or duly provided for, as the case may be,
until the principal amount of the Notes has been paid or duly provided for.
Interest shall be computed on the basis of a 360-day year consisting of twelve
30-day months.

      The interest rate borne by the Notes will be 6.375% per annum until the
Notes are paid in full.

      The interest payable on any Note which is punctually paid or duly provided
for on any Interest Payment Date shall be paid to the Person in whose name such
Note is registered at the close of business on the February 1 or August 1 (in
each case, whether or not a Business Day), respectively, immediately preceding
such Interest Payment Date (each, a "REGULAR RECORD DATE"). Interest payable on
any Note which is not punctually paid or duly provided for on any Interest
Payment Date therefor shall forthwith cease to be payable to the Person in whose
name such Note is registered at the close of business on the Regular Record Date
immediately preceding such Interest Payment Date, and such interest shall
instead be paid to the Person in whose name such Note is registered at the close
of business on the record date established for such payment by notice by or on
behalf of the Company to the Holders of the Notes mailed by first-class mail not
less than 15 days prior to such record date to their last addresses as they
shall appear upon the Security register, such record date to be not less than
five days preceding the date of payment of such defaulted interest.

      SECTION 2.5. PLACE OF PAYMENT. The place of payment where the Notes may be
presented or surrendered for payment, where the principal of and interest and
any other payments due on the Notes are payable, where the Notes may be
surrendered for registration of transfer or exchange and where notices and
demands to and upon the Company in respect of the Notes and the Indenture may be
served shall be in the Borough of Manhattan, The City of New York, and the
office or agency maintained by the Company for such purpose shall initially be
the Corporate Trust Office of the Trustee.

      At the option of the Company, interest on the Notes may be paid (i) by
check mailed to the address of the Person entitled thereto as such address shall
appear in the register of Holders of the Notes or (ii) at the expense of the
Company, by wire transfer to an account maintained by the Person entitled
thereto as specified in writing to the Trustee by such Person by the applicable
record date.

                                       4

<PAGE>

      SECTION 2.6. REDEMPTION. The Notes are redeemable, in whole or in part, at
the option of the Company at any time at a redemption price equal to the greater
of (i) 100% of the principal amount of such Notes, and (ii) as determined by the
Quotation Agent, the sum of the present values of the remaining scheduled
payments of principal and interest thereon (not including any portion of such
payments of interest accrued as of the date of redemption) discounted to the
date of redemption on a semiannual basis (assuming a 360-day year consisting of
twelve 30-day months) at the Adjusted Redemption Treasury Rate plus 20 basis
points plus, in each case, accrued interest thereon to the date of redemption.

      The Company shall have no obligation to redeem or purchase the Notes
pursuant to any sinking fund or analogous provisions or upon the happening of
any specified event or at the option of any Holder of the Notes.

      SECTION 2.7. ADDITIONAL AMOUNTS; CERTAIN TAX PROVISIONS. For purposes of
the Notes, Sections 12.1 and 12.2 of the Indenture are amended in their entirety
to read as follows:

      "SECTION 12.1. REDEMPTION UPON CHANGES IN WITHHOLDING TAXES. The Notes may
be redeemed, as a whole but not in part, at the option of the Company, upon not
less than 30 nor more than 60 days' notice (which notice shall be irrevocable),
at a redemption price equal to 100% of the principal amount thereof, together
with accrued interest, if any, to the redemption date and Additional Amounts (as
defined in Section 12.2), if any, if as a result of any amendment to, or change
in, the laws or regulations of Luxembourg or Bermuda or any political
subdivision or taxing authority thereof or therein having power to tax (a
"TAXING AUTHORITY"), or any change in the application or official interpretation
of such laws or regulations which amendment or change is announced or becomes
effective after the date the Notes are issued, the Company or Tyco has become or
will become obligated to pay Additional Amounts, on the next date on which any
amount would be payable with respect to the Notes, and such obligation cannot be
avoided by the use of reasonable measures available to the Company or Tyco, as
the case may be; provided, however, that (a) no such notice of redemption may be
given earlier than 60 days prior to the earliest date on which the Company or
Tyco, as the case may be, would be obligated to pay such Additional Amounts, and
(b) at the time such notice of redemption is given, such obligation to pay such
Additional Amounts remains in effect. Prior to the giving of any notice of
redemption described in this paragraph, the Company shall deliver to the Trustee
(i)(I) a certificate signed by two directors of the Company stating that the
obligation to pay Additional Amounts cannot be avoided by the Company taking
reasonable measures available to it or (II) a certificate signed by two
executive officers of Tyco stating that the obligation to pay Additional Amounts
cannot be avoided by Tyco taking reasonable measures available to it, as the
case may be, and (ii) a written opinion of independent legal counsel to the
Company or Tyco, as the case may be, of recognized standing to the effect that
the Company or Tyco, as the case may be, has or will become obligated to pay
Additional Amounts as a result of a change, amendment, official interpretation
or application described above and that the Company or Tyco, as the case may be,
cannot avoid the payment of such Additional Amounts by taking reasonable
measures available to it.

                                       5

<PAGE>

      SECTION 12.2. PAYMENT OF ADDITIONAL AMOUNTS. All payments made by the
Company, Tyco and any other Guarantor under or with respect to the Notes and the
Guarantees will be made free and clear of and without withholding or deduction
for or on account of any present or future taxes, duties, levies, imposts,
assessments or governmental charges of whatever nature imposed or levied by or
on behalf of any Taxing Authority ("TAXES"), unless the Company, Tyco or such
Guarantor, as the case may be, is required to withhold or deduct Taxes by law or
by the interpretation or administration thereof. In the event that the Company,
Tyco or such Guarantor is required to so withhold or deduct any amount for or on
account of any Taxes from any payment made under or with respect to the Notes or
the Guarantees, as the case may be, the Company, Tyco or such Guarantor, as the
case may be, will pay such additional amounts ("ADDITIONAL AMOUNTS") as may be
necessary so that the net amount received by each Holder of Notes (including
Additional Amounts) after such withholding or deduction will equal the amount
that such Holder would have received if such Taxes had not been required to be
withheld or deducted; provided that no Additional Amounts will be payable with
respect to a payment made to a Holder of Notes to the extent:

      (a) that any such Taxes would not have been so imposed but for the
existence of any present or former connection between such Holder and the Taxing
Authority imposing such Taxes (other than the mere receipt of such payment,
acquisition, ownership or disposition of such Notes or the exercise or
enforcement of rights under such Notes, the Guarantees or this Indenture);

      (b) of any estate, inheritance, gift, sales, transfer, or personal
property Taxes imposed with respect to such Notes, except as otherwise provided
herein;

      (c) that any such Taxes would not have been so imposed but for the
presentation of such Notes or Guarantees (where presentation is required) for
payment on a date more than 30 days after the date on which such payment became
due and payable or the date on which payment thereof is duly provided for,
whichever is later, except to the extent that the beneficiary or Holder thereof
would have been entitled to Additional Amounts had the Notes or Guarantees been
presented for payment on any date during such 30-day period; or

      (d) that such Holder would not be liable or subject to such withholding or
deduction of Taxes but for the failure to make a valid declaration of
non-residence or other similar claim for exemption, if (x) the making of such
declaration or claim is required or imposed by statute, treaty, regulation,
ruling or administrative practice of the relevant Taxing Authority as a
precondition to an exemption from, or reduction in, the relevant Taxes, and (y)
at least 60 days prior to the first payment date with respect to which the
Company, Tyco or such Guarantor shall apply this clause (d), the Company, Tyco
or such Guarantor shall have notified all Holders of Notes in writing that they
shall be required to provide such declaration or claim.

      The Company, Tyco or such Guarantor, as the case may be, will also (i)
make such withholding or deduction of Taxes and (ii) remit the full amount of
Taxes so deducted or withheld to the

                                       6

<PAGE>

relevant Taxing Authority in accordance with all applicable laws. The Company,
Tyco or such Guarantor, as the case may be, will use its reasonable best efforts
to obtain certified copies of tax receipts evidencing the payment of any Taxes
so deducted or withheld from each Taxing Authority imposing such Taxes. The
Company, Tyco or such Guarantor, as the case may be, will, upon request, make
available to the Holders of the Notes, within 60 days after the date the payment
of any Taxes so deducted or withheld is due pursuant to applicable law,
certified copies of tax receipts evidencing such payment by the Company, Tyco or
such Guarantor or if, notwithstanding the Company's, Tyco's or such Guarantor's
efforts to obtain such receipts, the same are not obtainable, other evidence of
such payments by the Company, Tyco or such Guarantor.

      At least 30 days prior to each date on which any payment under or with
respect to the Notes or Guarantees is due and payable, if the Company, Tyco or
such Guarantor will be obligated to pay Additional Amounts with respect to such
payment, the Company, Tyco or such Guarantor will deliver to the Trustee an
Officers' Certificate stating the fact that such Additional Amounts will be
payable, the amounts so payable and will set forth such other information as is
necessary to enable such Trustee to pay such Additional Amounts to Holders of
Notes on the payment date.

      In addition, the Company, Tyco or such Guarantor, as the case may be, will
pay any stamp, issue, registration, documentary or other similar taxes and
duties, including interest, penalties and Additional Amounts with respect
thereto, payable in Luxembourg, Bermuda or the United States or any political
subdivision or taxing authority of or in the foregoing in respect of the
creation, issue, offering, enforcement, redemption or retirement of the Notes or
the Guarantees.

      The foregoing provisions shall survive any termination or the discharge of
the Indenture and shall apply MUTATIS MUTANDIS to any jurisdiction in which any
successor Person to the Company, Tyco or such Guarantor, as the case may be, is
organized or is engaged in business for tax purposes or any political
subdivisions or taxing authority or agency thereof or therein; provided,
however, the date on which such Person becomes a successor to the Company, Tyco
or such Guarantor, as the case may be, shall be substituted for the date on
which the series of Notes was issued.

      Whenever in the Indenture, the Notes or the Guarantees there is mentioned,
in any context, the payment of principal (and premium, if any), redemption
price, interest or any other amount payable under or with respect to any Notes
or Guarantees, such mention shall be deemed to include mention of the payment of
Additional Amounts to the extent that, in such context, Additional Amounts are,
were or would be payable in respect thereof."

      SECTION 2.8. DENOMINATION. The Notes shall be issued in denominations of
$1,000 and integral multiples thereof.

      SECTION 2.9. CURRENCY. Principal and interest on the Notes shall be
payable in United States dollars.


                                        7

<PAGE>


      SECTION 2.10. NOTES TO BE ISSUED IN GLOBAL FORM; EXCHANGE FOR CERTIFICATED
NOTES. The Notes will be initially represented by one or more Notes in global
from (the "GLOBAL NOTE"). The Company hereby designates The Depository Trust
Company as the initial Depositary for the Global Note. The Global Note will be
deposited with the Trustee, as custodian for the Depositary. Unless and until it
is exchanged in whole or in part for Notes in certificated form, the Global Note
may not be transferred except as a whole by the Depositary to a nominee of the
Depositary or by a nominee of the Depositary to the Depositary or another
nominee of the Depositary or by the Depositary or any such nominee to a
successor Depositary for the Notes or a nominee of such successor Depositary.
The Depositary may surrender the Global Note in exchange in whole or in part for
Notes in certificated form on such terms as are acceptable to the Company and
Depositary.

      The Company may at any time in its sole discretion determine that all or
any portion of the Notes shall no longer be represented by a Note or Notes in
global form. In such event the Company shall execute, and the Trustee, upon
receipt of a written Company order (pursuant to Section 2.5 of the Indenture)
for the authentication and delivery of certificated Notes of like tenor, shall
authenticate and deliver Notes of like tenor in certificated form, in authorized
denominations and in an aggregate principal amount equal to the applicable
principal amount of the Global Note, in exchange for such Global Note (or the
applicable portion thereof).

      SECTION 2.11. FORM OF NOTES. The Notes shall be substantially in the form
attached as Exhibit A hereto.

      SECTION 2.12. DEFEASANCE AND COVENANT DEFEASANCE. The provisions of
Article Nine of the Indenture shall apply to the Notes.

      SECTION 2.13. ISSUANCE OF ADDITIONAL NOTES. For purposes of the Notes,
Section 7.1 of the Indenture is hereby amended by inserting therein a new
Section 7.1(h) to read as follows:

      "(h) to issue additional Securities of any series in the future pursuant
to Section 2.5 of this Indenture; PROVIDED, that such additional Securities have
the same terms as, and be deemed part of the same series as, the applicable
series of Securities issued hereunder."

      SECTION 2.14. DEFINITION OF PERMITTED SUBSIDIARY INDEBTEDNESS. Clause (vi)
of the definition of "Permitted Subsidiary Indebtedness" in Section 1.1 of the
Indenture is amended by inserting after the phrase "Acquired Indebtedness that
by its terms is not" the following phrase:

      ", at the time it becomes Acquired Indebtedness or within 180 days
thereafter,"

      SECTION 2.15. DEFINITION OF RESTRICTED SUBSIDIARY. The definition of
"Restricted Subsidiary" in Section 1.1 of the Indenture is amended in its
entirety to read as follows:


                                       8

<PAGE>

       ""RESTRICTED SUBSIDIARY" means any Subsidiary of the Company which owns
or leases a Principal Property."


                                    ARTICLE 3

                            MISCELLANEOUS PROVISIONS

      SECTION 3.1. ADOPTION, RATIFICATION AND CONFIRMATION. The Indenture, as
supplemented and amended by this Supplemental Indenture No. 15, is in all
respects hereby adopted, ratified and confirmed.

      SECTION 3.2. COUNTERPARTS. This Supplemental Indenture No. 15 may be
executed in any number of counterparts, each of which when so executed shall be
deemed an original; and all such counterparts shall together constitute but one
and the same instrument.

      SECTION 3.3. GOVERNING LAW. THIS SUPPLEMENTAL INDENTURE NO. 15, EACH NOTE
AND EACH GUARANTEE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO THE CHOICE OF LAW PRINCIPLES
THEREOF.



                                        9

<PAGE>


      IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture No. 15 to be duly executed as of the day and year first written above.

                                    TYCO INTERNATIONAL GROUP S.A.


                                    By: /s/ Richard W. Brann
                                       ----------------------------------------
                                       Name:   Richard W. Brann
                                       Title:  Managing Director


                                    TYCO INTERNATIONAL LTD.


                                    By: /s/ Mark H. Swartz
                                       ----------------------------------------
                                       Name:   Mark H. Swartz
                                       Title:  Executive Vice President and
                                               Chief Financial Officer


<PAGE>



                                    THE BANK OF NEW YORK, Trustee


                                    By: /s/ Deirdra N. Ross
                                       ----------------------------------------
                                       Name:  Deirdra N. Ross
                                       Title: Assistant Treasurer


<PAGE>



                                                                       EXHIBIT A

                          [FORM OF FACE OF GLOBAL NOTE]

      Unless this certificate is presented by an authorized representative of
The Depository Trust Company, a New York corporation ("DTC"), to the Issuer or
its agent for registration of transfer, exchange, or payment, and any
certificate issued is registered in the name of Cede & Co. or in such other name
as is requested by an authorized representative of DTC (and any payment is made
to Cede & Co. or to such other entity as is requested by an authorized
representative of DTC), ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered owner
hereof, Cede & Co., has an interest herein.

      Unless and until it is exchanged in whole or in part for Notes in
definitive registered form, this Note may not be transferred except as a whole
by the Depositary to the nominee of the Depositary or by a nominee of the
Depositary to the Depositary or another nominee of the Depositary or by the
Depositary or any such nominee to a successor Depositary or a nominee of such
successor Depositary.


                          TYCO INTERNATIONAL GROUP S.A.

                              6.375% Note due 2006

No.

$                                                          CUSIP:   902118 AX 6


      TYCO INTERNATIONAL GROUP S.A., a Luxembourg company (the "ISSUER"), for
value received, hereby promises to pay to CEDE & CO. or registered assigns, the
principal sum of [ ] on February 15, 2006, at the office or agency of the Issuer
in the Borough of Manhattan, The City of New York, in such coin or currency of
the United States of America as at the time of payment shall be legal tender for
the payment of public and private debts, and to pay semiannually on February 15
and August 15 of each year (each, an "INTEREST PAYMENT DATE"; provided, however,
that if an Interest Payment Date would otherwise be a day that is not a Business
Day, such Interest Payment Date shall be the next succeeding Business Day but no
additional interest shall be paid in respect of such intervening period),
commencing August 15, 2001, the amount of interest on said principal sum at said
office or agency, in like coin or currency, at the rate per annum specified in
the title of this Note, from February 21, 2001 or from the most recent Interest
Payment Date to which interest has been paid or duly provided for until said
principal sum has been paid or duly provided for. Interest


                                       A-1

<PAGE>

shall be computed on the basis of a 360-day year consisting of twelve 30-day
months. For purposes of this Note, "BUSINESS DAY" means any day other than a
Saturday, a Sunday or a day on which banking institutions in The City of New
York are authorized or obligated by law, regulation or executive order to be
closed.

      The interest payable on any Interest Payment Date which is punctually paid
or duly provided for on such Interest Payment Date will be paid to the Person in
whose name this Note is registered at the close of business on the February 1 or
August 1 (in each case, whether or not a Business Day), as the case may be
(each, a "REGULAR RECORD DATE"), immediately preceding such Interest Payment
Date. Interest payable on this Note which is not punctually paid or duly
provided for on any Interest Payment Date therefor shall forthwith cease to be
payable to the Person in whose name this Note is registered at the close of
business on the Regular Record Date immediately preceding such Interest Payment
Date, and such interest shall instead be paid to the Person in whose name this
Note is registered at the close of business on the record date established for
such payment by notice by or on behalf of the Issuer to the Holders of the Notes
mailed by first-class mail not less than 15 days prior to such record date to
their last addresses as they shall appear upon the Security register, such
record date to be not less than five days preceding the date of payment of such
defaulted interest. At the option of the Issuer, interest on the Notes may be
paid (i) by check mailed to the address of the Person entitled thereto as such
address shall appear in the register of Holders of the Notes or (ii) at the
expense of the Issuer, by wire transfer to an account maintained by the Person
entitled thereto as specified in writing to the Trustee by such Person by the
applicable record date of the Notes.

      Reference is made to the further provisions of this Note set forth on the
reverse hereof. Such further provisions shall for all purposes have the same
effect as though fully set forth at this place.

      This Note shall not be valid or become obligatory for any purpose until
the certificate of authentication hereon shall have been signed by the Trustee
under the Indenture referred to on the reverse hereof.


                                       A-2

<PAGE>


      IN WITNESS WHEREOF, TYCO INTERNATIONAL GROUP S.A. has caused this
instrument to be signed by its duly authorized Managing Directors.

Dated:  February 21, 2001


                                    TYCO INTERNATIONAL GROUP S.A.


                                    By:
                                        ---------------------------------------
                                        Title:


                                    By:
                                        ---------------------------------------
                                        Title:



                                       A-3

<PAGE>



                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION


      This is one of the Securities of the series designated herein referred to
in the within-mentioned Indenture.

Dated:  February 21, 2001


                                       THE BANK OF NEW YORK,
                                         as Trustee


                                       By:
                                           ------------------------------------
                                                    Authorized Signatory



                                       A-4

<PAGE>



                                    GUARANTEE


      For value received, TYCO INTERNATIONAL LTD. hereby absolutely,
unconditionally and irrevocably guarantees to the holder of this Note the
payment of principal of, and interest on, the Note upon which this Guarantee is
endorsed in the amounts and at the time when due and payable whether by
declaration thereof, or otherwise, and interest on the overdue principal and
interest, if any, of such Note, if lawful, and the payment or performance of all
other obligations of the Issuer under the Indenture or the Notes, to the holder
of such Note and the Trustee, all in accordance with and subject to the terms
and limitations of such Note and Article Thirteen of the Indenture. This
Guarantee will not become effective until the Trustee duly executes the
certificate of authentication on this Note. This Guarantee shall be governed by
and construed in accordance with the laws of the State of New York, without
regard to conflict of law principles thereof. All references in this Guarantee
to interest shall include any Additional Amounts.

Dated:  February 21, 2001


                                   TYCO INTERNATIONAL LTD.


                                   By:
                                       ----------------------------------------
                                       Name:   Mark H. Swartz
                                       Title:  Executive Vice President and
                                               Chief Financial Officer



                                       A-5

<PAGE>



                        [FORM OF REVERSE OF GLOBAL NOTE]

                          TYCO INTERNATIONAL GROUP S.A.

                              6.375% Note due 2006


      1. INDENTURE. (a) This Note is one of a duly authorized issue of notes of
the Issuer (hereinafter called the "NOTES") of a series designated as the 6.375%
Notes due 2006 of the Issuer, initially limited in aggregate principal amount to
$1,000,000,000, all issued or to be issued under and pursuant to an indenture,
dated as of June 9, 1998, as amended and supplemented by Supplemental Indenture
No. 15, dated as of February 21, 2001 (as so amended and supplemented, the
"INDENTURE"), among the Issuer, Tyco International Ltd. ("TYCO") and The Bank of
New York, as Trustee (herein called the "TRUSTEE"), to which Indenture and all
indentures supplemental thereto reference is hereby made for a description of
the rights, limitations of rights, obligations, duties and immunities thereunder
of the Issuer, Tyco, the Trustee and the Holders of the Notes.

      (b) Other debentures, notes, bonds or other evidences of indebtedness
(together with the Notes, hereinafter called the "SECURITIES") may be issued
under the Indenture in one or more series, which different series may be issued
in various aggregate principal amounts, may mature at different times, may bear
interest (if any) at different rates, may be subject to different redemption
provisions (if any), may be subject to different sinking, purchase or analogous
funds (if any) and may otherwise vary from the Notes and each other, as in the
Indenture provided.

      (c) All capitalized terms used in this Note which are defined in the
Indenture and not otherwise defined herein shall have the meanings assigned to
them in the Indenture.

      2. AMENDMENTS AND WAIVERS. (a) The Indenture contains provisions
permitting the Issuer and the Trustee, with the consent of the Holders of not
less than a majority in aggregate principal amount of the Securities at the time
Outstanding of all series to be affected (voting as one class), evidenced as in
the Indenture provided, to execute supplemental indentures adding any provisions
to or changing in any manner or eliminating any of the provisions of the
Indenture or of any supplemental indenture or modifying in any manner the rights
of the Holders of the Securities of each such series; provided, that no such
supplemental indenture shall (i) extend the final maturity of any Security, or
reduce the principal amount thereof, or reduce the rate or extend the time of
payment of interest thereon, or reduce any amount payable on redemption thereof
or reduce the amount of the principal of an Original Issue Discount Security
that would be due and payable upon an acceleration of the maturity thereof
pursuant to Section 4.1 of the Indenture or the amount thereof provable in
bankruptcy pursuant to Section 4.2 of the Indenture, or impair or affect the
rights of any Holder to institute suit for the payment thereof, without the
consent of the Holder of each Security so affected, or


                                      a-6

<PAGE>

(ii) reduce the aforesaid percentage of Securities, the Holders of which are
required to consent to any such supplemental indenture, without the consent of
the Holder of each Security affected.

      (b) It is also provided in the Indenture that, with respect to certain
defaults or Events of Default regarding the Securities of any series, prior to
any declaration accelerating the maturity of such Securities, the Holders of a
majority in aggregate principal amount Outstanding of the Securities of such
series (or, in the case of certain defaults or Events of Default, all or certain
series of the Securities) may on behalf of the Holders of all the Securities of
such series (or all or certain series of the Securities, as the case may be)
waive any such past default or Event of Default and its consequences. The
preceding sentence shall not, however, apply to a default in the payment of the
principal of, premium, if any, or interest on any of the Securities. Any such
consent or waiver by the Holder of this Note (unless revoked as provided in the
Indenture) shall be conclusive and binding upon such Holder and upon all future
Holders and owners of this Note and any Notes which may be issued in exchange or
substitution herefor, irrespective of whether or not any notation thereof is
made upon this Note or such other Notes.

      3. OBLIGATION TO PAY PRINCIPAL, PREMIUM, IF ANY, AND INTEREST. No
reference herein to the Indenture and no provision of this Note or of the
Indenture shall alter or impair the obligation of the Issuer, Tyco or any other
obligor on the Notes, which is absolute and unconditional, to pay the principal
of, premium, if any, and interest on this Note in the manner, at the respective
times, at the rate, at the place and in the coin or currency herein prescribed.

      4. REDEMPTION. This Note may be redeemed, in whole or in part, at the
option of the Issuer at any time at a redemption price equal to the greater of
(i) 100% of the principal amount of this Note, and (ii) as determined by the
Quotation Agent, the sum of the present values of the remaining scheduled
payments of principal and interest thereon (not including any portion of such
payments of interest accrued as of the date of redemption) discounted to the
date of redemption on a semiannual basis (assuming a 360-day year consisting of
twelve 30-day months) at the Adjusted Redemption Treasury Rate plus 20 basis
points plus, in each case, accrued interest thereon to the date of redemption.
This Note is also subject to redemption to the extent provided in Article Twelve
of the Indenture.

      "ADJUSTED REDEMPTION TREASURY RATE" means, with respect to any redemption
date, the annual rate equal to the semiannual equivalent yield to maturity or
interpolated (on a 30/360 day count basis) yield to maturity of the Comparable
Redemption Treasury Issue, assuming a price for the Comparable Redemption
Treasury Issue (expressed as a percentage of its principal amount) equal to the
Comparable Redemption Treasury Price for such redemption date.

      "BUSINESS DAY" means any day other than a Saturday, a Sunday or a day on
which banking institutions in The City of New York are authorized or obligated
by law, executive order or governmental decree to be closed.


                                       A-7

<PAGE>


      "COMPARABLE REDEMPTION TREASURY ISSUE" means the United States Treasury
security selected by the Quotation Agent as having a maturity comparable to the
remaining term of the Notes to be redeemed that will be utilized at the time of
selection and in accordance with customary financial practice in pricing new
issues of corporate debt securities of comparable maturity to the remaining term
of such Notes.

      "COMPARABLE REDEMPTION TREASURY PRICE" means, with respect to any
redemption date, (i) the average of the Redemption Reference Treasury Dealer
Quotations for such redemption date, after excluding the highest and lowest such
Redemption Reference Treasury Dealer Quotations (unless there is more than one
highest or lowest quotation, in which case only one such highest and/or lowest
quotation shall be excluded), or (ii) if the Quotation Agent obtains fewer than
four such Redemption Reference Treasury Dealer Quotations, the average of all
such Redemption Reference Treasury Dealer Quotations.

      "QUOTATION AGENT" means a Redemption Reference Treasury Dealer appointed
as such agent by the Company.

      "REDEMPTION REFERENCE TREASURY DEALER" means each of Banc of America
Securities LLC and Lehman Brothers Inc. and three other primary U.S. Government
securities dealers in The City of New York selected by the Company.

      "REDEMPTION REFERENCE TREASURY DEALER QUOTATIONS" means, with respect to
each Redemption Reference Treasury Dealer and any redemption date, the offer
price for the Comparable Redemption Treasury Issue (expressed in each case as a
percentage of its principal amount) for settlement on the redemption date quoted
in writing to the Quotation Agent by such Redemption Reference Treasury Dealer
at 5:00 p.m., New York City time, on the third Business Day preceding such
redemption date.

      5. CERTAIN COVENANTS. The Indenture restricts the Issuer's ability to
merge, consolidate or sell substantially all of its assets. In addition, the
Issuer is obliged to abide by certain covenants, including covenants limiting
the amount of liens it may incur, as well as its ability to enter into sale and
leaseback transactions, a covenant limiting the ability of its subsidiaries to
incur indebtedness, and a covenant requiring it to pay or discharge all taxes,
all as more fully described in the Indenture. All of such covenants are subject
to the covenant defeasance procedures outlined in the Indenture.

      6. EFFECT OF EVENT OF DEFAULT. If an Event of Default shall have occurred
and be continuing under the Indenture, the principal hereof may be declared, and
upon such declaration shall become, due and payable in the manner, with the
effect and subject to the conditions provided in the Indenture.


                                       A-8

<PAGE>


      7. DEFEASANCE. The Indenture contains provisions for defeasance and
covenant defeasance at any time of the indebtedness on this Note upon compliance
by the Issuer with certain conditions set forth therein.

      8. DENOMINATIONS; TRANSFER. (a) The Notes are issuable in registered form
without coupons in denominations of $1,000 and any multiple of $1,000 at the
office or agency of the Issuer in the Borough of Manhattan, The City of New
York, and in the manner and subject to the limitations provided in the
Indenture.

      (b) Upon due presentment for registration of transfer of this Note at the
office or agency of the Issuer in the Borough of Manhattan, The City of New
York, a new Note or Notes of authorized denominations for an equal aggregate
principal amount will be issued to the transferee in exchange therefor, subject
to the limitations provided in the Indenture. This Note may also be surrendered
for exchange at the aforesaid office or agency for Notes in other authorized
denominations in an equal aggregate principal amount. No service charge shall be
made for any registration of transfer or any exchange of the Notes, except that
the Issuer may require payment of any tax or other governmental charge imposed
in connection therewith.

      (c) A certificate in global form representing all of a portion of the
Notes may not be transferred except as a whole by the Depositary for such series
to a nominee of such Depositary or by a nominee of such Depositary to such
Depositary or another nominee of such Depositary or by such Depositary or any
such nominee to a successor Depositary for such Notes or a nominee of such
successor Depositary.

      9. HOLDER AS OWNER. The Issuer, Tyco, the Trustee and any authorized agent
of the Issuer, Tyco or the Trustee may deem and treat the registered Holder
hereof as the absolute owner of this Note (whether or not this Note shall be
overdue and notwithstanding any notation of ownership or other writing hereon),
for the purpose of receiving payment of, or on account of, the principal hereof
and, subject to the provisions on the face hereof, interest hereon, and for all
other purposes, and none of the Issuer, Tyco or the Trustee or any authorized
agent of the Issuer, Tyco or the Trustee shall be affected by any notice to the
contrary.

      10. NO LIABILITY OF CERTAIN PERSONS. No recourse under or upon any
obligation, covenant or agreement of the Issuer or Tyco in the Indenture or any
indenture supplemental thereto or in any Note, or because of the creation of any
indebtedness represented thereby, shall be had against any incorporator, or any
past, present or future shareholder, officer or director, as such, of the
Issuer, Tyco or of any successor corporation of either of them, either directly
or through the Issuer, Tyco or any successor corporation, under any rule of law,
statute or constitutional provision or by the enforcement of any assessment or
by any legal or equitable proceeding or otherwise, all such liability being
expressly waived and released by the acceptance hereof and as part of the
consideration for the issue hereof.



                                       A-9

<PAGE>


      11. GUARANTEES. The payment and performance of all obligations of the
Issuer under the Indenture and this Note are fully and unconditionally
guaranteed to the holder of this Note by Tyco, as provided in the related
Guarantee and the Indenture.

      12. GOVERNING LAW. THE LAWS OF THE STATE OF NEW YORK GOVERN THE INDENTURE
AND THIS NOTE (AND THE GUARANTEE ENDORSED HEREON).

      13. ADDITIONAL AMOUNTS. The Issuer and Tyco are obligated to pay
Additional Amounts on this Note to the extent provided in Article Twelve of the
Indenture.



                                      A-10

<PAGE>


      FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and
transfer(s) unto:


PLEASE INSERT TAXPAYER
IDENTIFICATION NUMBER OF ASSIGNEE

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

PLEASE PRINT OR TYPE NAME AND ADDRESS, INCLUDING ZIP CODE,
OF ASSIGNEE

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the within Note of Tyco International Group S.A. and all rights thereunder and
hereby irrevocably constitutes and appoints such person attorney to transfer
such Note on the books of Tyco International Group S.A., with full power of
substitution in the premises.


Dated:

                                                   ----------------------------
                                                            Signature


NOTICE:    THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH
           THE NAME AS WRITTEN UPON THE FACE OF THE WITHIN
           INSTRUMENT IN EVERY PARTICULAR, WITHOUT ALTERATION OR
           ENLARGEMENT OR ANY CHANGE WHATEVER.  THE SIGNATURE
           SHOULD BE GUARANTEED BY A COMMERCIAL BANK OR TRUST
           COMPANY, A MEMBER ORGANIZATION OF A NATIONAL STOCK
           EXCHANGE OR BY SUCH OTHER ENTITY WHOSE SIGNATURE IS ON
           FILE WITH AND ACCEPTABLE TO THE TRANSFER AGENT.


                                      A-11