<PAGE>
 
                                                                    EXHIBIT 10.1

                               PINKERTON'S, INC.

                              SECOND AMENDMENT TO
                          REVOLVING CREDIT AGREEMENT


         This SECOND AMENDMENT TO REVOLVING CREDIT AGREEMENT (this "AMENDMENT")
is dated as of June 27, 1997 and entered into by and among Pinkerton's, Inc., a
Delaware corporation (the "COMPANY"), the Designated Subsidiaries (as defined in
the Credit Agreement referred to below), the financial institutions listed on
the signature pages hereof (the "LENDERS") and Citicorp USA, Inc., as agent for
the Lenders (the "AGENT"), and, for purposes of Section 5 hereof, the Subsidiary
Guarantors listed on the signature pages hereof, and is made with reference to
that certain Revolving Credit Agreement dated as of November 21, 1995 as amended
to the date hereof (the "CREDIT AGREEMENT"), by and among the Company, the
Designated Subsidiaries, the Lenders and the Agent.  Capitalized terms used
herein without definition shall have the same meanings herein as set forth in
the Credit Agreement.

                                RECITALS

         WHEREAS, the Company, the Designated Subsidiaries and the Lenders have
entered into the Credit Agreement, pursuant to which certain credit facilities
were extended to the Company and the Designated Subsidiaries;

         WHEREAS, the Company wishes to finance its acquisition of the assets of
the Enterprise Accounts Division of Sensormatic Electronics Corporation in part
through the Credit Agreement; and

         WHEREAS, the Company, the Designated Subsidiaries, and the Lenders
desire to amend the Credit Agreement to (i) increase the Commitment from $70
million to $100 million; (ii) increase the Senior Debt allowed from $42,850,000
to $100,000,000, and (iii) make certain other amendments as set forth below;

         NOW, THEREFORE, in consideration of the premises and the agreements,
provisions and covenants herein contained, the parties hereto agree as follows:
<PAGE>
 
         SECTION 1.  AMENDMENTS TO THE CREDIT AGREEMENT


         1.1  AMENDMENTS TO ARTICLE I:  DEFINITIONS AND ACCOUNTING TERMS
              ----------------------------------------------------------
 
         A.   Section 1.01 of the Credit Agreement is hereby amended by deleting
the definition of "Financial Institution" therein in its entirety and
substituting the following therefor:

         "'FINANCIAL INSTITUTION' means the financial institutions listed on
         Schedule A of the Second Amendment to the Credit Agreement."

         B.   Section 1.01 of the Credit Agreement is hereby amended by deleting
the definition of "Senior Notes" in its entirety and substituting the following
therefor:

         "'SENIOR NOTES' means the $60,000,000 aggregate principal amount of
         10.35% Senior Notes due June 15, 2000 issued by the Company pursuant to
         the Senior Note Purchase Agreement and any Senior Notes issued by the
         Company pursuant to the New Note Purchase Agreement."

         C.   Section 1.01 of the Credit Agreement is hereby amended by adding a
new definition as follows:

         "'NEW NOTE PURCHASE AGREEMENT' means one or more note purchase
         agreements entered into between the Company and purchasers of the
         Company's unsecured senior notes, which note purchase agreements shall
         contain principal, interest and repayment terms as the Company and such
         purchasers shall agree upon, and other covenants and conditions no more
         restrictive on the Company and its Subsidiaries than the terms,
         covenants and conditions set forth in the Senior Note Purchase
         Agreement, and which note purchase agreement shall be satisfactory in
         form and substance to the Majority Lenders, such approval of the
         Majority Lenders not to be unreasonably withheld."

         1.2  AMENDMENTS TO ARTICLE II: AMOUNTS AND TERMS OF THE ADVANCES
              ------------------------------------------------------------

         A.   Subsection 2.01(a) of the Credit Agreement is hereby amended by
deleting "on the signature pages hereof" and substituting "on Schedule A of the
Second Amendment to the Credit Agreement" therefor.

                                       2
<PAGE>
 
         1.3  AMENDMENTS TO ARTICLE V: COVENANTS OF THE COMPANY
              -------------------------------------------------

         A.   Subsection 5.02(b)(ii) of the Credit Agreement is hereby amended
by deleting "$42,850,000" and substituting "$100,000,000" therefor.

         B.   Subsection 5.02(e)(iii) of the Credit Agreement is hereby amended
by (a) adding the following after "Persons": "(or, in the case of an acquisition
of assets, an operating division of a Person)" and (b) adding the following
after "$50,000,000":  "provided that such amount for the Company's fiscal year
ending December 26, 1997 shall be $100,000,000 if (and only if) the Company
completes the acquisition of substantially all of the assets of the Enterprise
Accounts Division of Sensormatic Electronics Corporation in such fiscal year.

         C.   Subsection 5.02(i) of the Credit Agreement is hereby amended by
replacing the period at the end of said section by a comma, and adding the
following after such comma:

         "or enter into or otherwise agree to any amendment or other variation
         of the New Note Purchase Agreement that would make the New Note
         Purchase Agreement more restrictive or would otherwise materially
         adversely affect the interests of the Lenders or the Issuing Lender
         under this Agreement."

         SECTION 2.  REALLOCATION OF COMMITMENTS AND A ADVANCES

         On the Second Amendment Effective Date (as defined below), each Lender
that has, after giving effect to this Amendment, a larger percentage share of
the Aggregate Commitments than it had prior to the effectiveness of this
Amendment will, through the Agent, make a payment to the Lenders with smaller
percentage shares of the Aggregate Commitments after giving effect to this
Amendment, such that each Lender's pro rata share of outstanding A Advances and
Letter of Credit Usage is reallocated in accordance with such Lender's pro rata
share of the new Aggregate Commitments. Prior to the Effective Date, the Agent
will notify each Lender of the amount to be paid or received by it pursuant to
this Section 2 on the Effective Date. In the event that any such payment of any
A Advance that is a Eurocurrency Rate Advance occurs on a date other than the
end of the Eurocurrency Rate Interest Period for such Advance, the Company will
indemnify each Lender paying and/or receiving such amounts against any loss (not
including loss of anticipated profits), cost or expense incurred by such Lender
as a result of such payment.

         SECTION 3.  CONDITIONS TO EFFECTIVENESS

         Section 1 of this Amendment shall become effective only upon the
satisfaction of all of the following conditions precedent (the date of
satisfaction of such conditions being referred to herein as the "SECOND
AMENDMENT EFFECTIVE DATE"):

                                       3
<PAGE>
 
         A.   On or before the Second Amendment Effective Date, the Company
shall deliver to Lenders (or to Agent for Lenders with sufficient originally
executed copies, where appropriate, for each Lender and its counsel) the
following, each, unless otherwise noted, dated the Second Amendment Effective
Date:

              1. Certified copies of its Certificate of Incorporation, together
    with a good standing certificate from the Secretary of State of the State of
    Delaware, each dated a recent date prior to the Second Amendment Effective
    Date;

              2. Copies of its Bylaws, certified as of the Second Amendment
    Effective Date by its corporate secretary or an assistant secretary;

              3. Resolutions of its Board of Directors approving and authorizing
    the execution, delivery, and performance of this Amendment certified as of
    the Second Amendment Effective Date by its corporate secretary or an
    assistant secretary as being in full force and effect without modification
    or amendment;

              4. Signature and incumbency certificates of its officers executing
    this Amendment; and

              5. Executed copies of this Amendment.

         B.   The Lenders and their respective counsel shall have received
originally executed copies of the favorable written opinion of C. Michael
Carter, Esq., counsel for the Company, in form and substance reasonably
satisfactory to Agent and its counsel, dated as of the Second Amendment
Effective Date and setting forth substantially the matters in the opinions
designated in Annex A to this Amendment and as to such other matters as the
Agent acting on behalf of the Lenders may reasonably request.

         C.   On or before the Second Amendment Effective Date, all corporate
and other proceedings taken or to be taken in connection with the transactions
contemplated hereby and all documents incidental thereto not previously found
acceptable by the Agent, acting on behalf of the Lenders, and its counsel shall
be satisfactory in form and substance to the Agent and such counsel, and the
Agent and such counsel shall have received all such counterpart originals or
certified copies of such documents as the Agent may reasonably request.

                                       4
<PAGE>
 
         SECTION 4.  COMPANY'S REPRESENTATIONS AND WARRANTIES

         In order to induce Lenders to enter into this Amendment and to amend
the Credit Agreement in the manner provided herein, Company represents and
warrants to each Lender that the following statements are true, correct and
complete:

         A.   CORPORATE POWER AND AUTHORITY.  Each of the Company and the
Designated Subsidiaries has all requisite corporate power and authority to enter
into this Amendment and to carry out the transactions contemplated by, and
perform its obligations under, the Credit Agreement as amended by this Amendment
(the "AMENDED AGREEMENT").

         B.   AUTHORIZATION OF AGREEMENTS.  The execution and delivery of this
Amendment and the performance of the Amended Agreement have been duly authorized
by all necessary corporate action on the part of the Company and the Designated
Subsidiaries.

         C.   NO CONFLICT.  The execution and delivery by the Company and the
Designated Subsidiaries of this Amendment and the performance by the Company and
the Designated Subsidiaries of the Amended Agreement do not and will not (i)
violate any provision of any law or any governmental rule or regulation
applicable to Company or any of its Subsidiaries, the Certificate or Articles of
Incorporation or Bylaws of the Company or any of its Subsidiaries or any order,
judgment or decree of any court or other agency of government binding on Company
or any of its Subsidiaries, (ii) conflict with, result in a breach of or
constitute (with due notice or lapse of time or both) a default under any
Contractual Obligation of the Company or any of its Subsidiaries, (iii) result
in or require the creation or imposition of any Lien upon any of the properties
or assets of the Company or any of its Subsidiaries (other than Liens created
under any of the Loan Documents in favor of the Agent on behalf of the Lenders),
or (iv) require any approval of stockholders or any approval or consent of any
Person under any Contractual Obligation of Company or any of its Subsidiaries

         D.   GOVERNMENTAL CONSENTS.  The execution and delivery by the Company
and the Designated Subsidiaries of this Amendment and the performance by the
Company and the Designated Subsidiaries of the Amended Agreement do not and will
not require any registration with, consent or approval of, or notice to, or
other action to, with or by, any federal, state or other governmental authority
or regulatory body.

         E.   BINDING OBLIGATION.  This Amendment and the Amended Agreement have
been duly executed and delivered by the Company and the Designated Subsidiaries
and are the legally valid and binding obligations of the Company and the
Designated Subsidiaries, enforceable against the Company and the Designated
Subsidiaries in accordance with their respective terms, except as may be limited
by bankruptcy, insolvency, reorganization, moratorium or similar laws relating
to or limiting creditors' rights generally or by equitable principles relating
to enforceability.

                                       5
<PAGE>

         F.   INCORPORATION OF REPRESENTATIONS AND WARRANTIES FROM CREDIT
AGREEMENT.  The representations and warranties contained in Article IV of the
Credit Agreement are and will be true, correct and complete in all material
respects on and as of the Second Amendment Effective Date to the same extent as
though made on and as of that date, except to the extent such representations
and warranties specifically relate to an earlier date, in which case they were
true, correct and complete in all material respects on and as of such earlier
date.

         G.   ABSENCE OF DEFAULT.  No event has occurred and is continuing or
will result from the consummation of the transactions contemplated by this
Amendment that would constitute an Event of Default or a Potential Event of
Default.


         SECTION 5.  ACKNOWLEDGEMENT AND CONSENT

         Each of the Subsidiary Guarantors is a party to a Subsidiary Guaranty
and such Subsidiary Guarantor has guarantied the Obligations.

         Each Subsidiary Guarantor hereby acknowledges that it has reviewed the
terms and provisions of the Credit Agreement and this Amendment and consents to
the amendment of the Credit Agreement effected pursuant to this Amendment.  Each
Subsidiary Guarantor hereby confirms that the Subsidiary Guaranty to which it is
a party or otherwise bound will continue to guaranty to the fullest extent
possible the payment and performance of all "Subsidiary Guarantied Obligations"
as such term is defined in the applicable Subsidiary Guaranty, including without
limitation the payment and performance of all such "Subsidiary Guarantied
Obligations" in respect of the Obligations of Company and the Designated
Subsidiaries now or hereafter existing under or in respect of the Amended
Agreement.

         Each Subsidiary Guarantor acknowledges and agrees that Subsidiary
Guaranty to which it is a party or otherwise bound shall continue in full force
and effect and that all of its obligations thereunder shall be valid and
enforceable and shall not be impaired or limited by the execution or
effectiveness of this Amendment.  Each Subsidiary Guarantor represents and
warrants that all representations and warranties contained in the Amended
Agreement and the Subsidiary Guaranty to which it is a party or otherwise bound
are true, correct and complete in all material respects on and as of the Second
Amendment Effective Date to the same extent as though made on and as of that
date, except to the extent such representations and warranties specifically
relate to an earlier date, in which case they were true, correct and complete in
all material respects on and as of such earlier date.

         Each Subsidiary Guarantor acknowledges and agrees that (i)
notwithstanding the conditions to effectiveness set forth in this Amendment,
such Subsidiary Guarantor is not required by the terms of the Credit Agreement
or any other Loan Document to consent to the amendments to the Credit Agreement
effected pursuant to this Amendment and (ii) nothing in the Credit Agreement,
this Amendment or any other Loan Document shall be deemed to require the consent
of such Subsidiary Guarantor to any future amendments to the Credit Agreement.

                                       6
<PAGE>

         SECTION 6.  MISCELLANEOUS

         A.   REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND THE OTHER LOAN
DOCUMENTS.

         (i) On and after the Second Amendment Effective Date, each reference in
    the Credit Agreement to "this Agreement", "hereunder", "hereof", "herein" or
    words of like import referring to the Credit Agreement, and each reference
    in the other Loan Documents to the "Credit Agreement", "thereunder",
    "thereof" or words of like import referring to the Credit Agreement shall
    mean and be a reference to the Amended Agreement.

         (ii) Except as specifically amended by this Amendment, the Credit
    Agreement and the other Loan Documents shall remain in full force and effect
    and are hereby ratified and confirmed.

         (iii)  The execution, delivery and performance of this Amendment shall
    not, except as expressly provided herein, constitute a waiver of any
    provision of, or operate as a waiver of any right, power or remedy of Agent
    or any Lender under, the Credit Agreement or any of the other Loan
    Documents.

         B.   FEES AND EXPENSES.  Company acknowledges that all costs, fees and
expenses as described in Section 9.04 of the Credit Agreement incurred by Agent
and its counsel with respect to this Amendment and the documents and
transactions contemplated hereby shall be paid by the Company in accordance with
Section 9.04.

         C.   HEADINGS.  Section and subsection headings in this Amendment are
included herein for convenience of reference only and shall not constitute a
part of this Amendment for any other purpose or be given any substantive effect.

         D.   APPLICABLE LAW.  THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF
THE PARTIES HEREUNDER SHALL BE GOVERNED BY, AND SHALL BE CONSTRUED AND ENFORCED
IN ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD
TO CONFLICTS OF LAWS PRINCIPLES.

         E.   COUNTERPARTS; EFFECTIVENESS.  This Amendment may be executed in
any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed and delivered shall be deemed an
original, but all such counterparts together shall constitute but one and the
same instrument; signature pages may be detached from multiple separate
counterparts and attached to a single counterpart so that all signature pages
are physically attached to the same document.  This Amendment shall become
effective upon the execution of a counterpart hereof by (i) the Majority
Lenders, (ii) each Lender whose
                                       7
<PAGE>

Commitment will be increased as a result of this Amendment, and (iii) each of
the other parties hereto and receipt by Company and Agent of written or
telephonic notification of such execution and authorization of delivery thereof.


                 [Remainder of page intentionally left blank]
 

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<PAGE>
 
         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered by their respective officers thereunto duly
authorized as of the date first written above.

                               PINKERTON'S, INC.


                               By:     /s/ James P. McCloskey
                                   ----------------------------
                               Title:   EVP & CFO
                                      -------------------------


                               PINKERTON'S GMBH


                               By:     /s/ James P. McCloskey
                                   --------------------------------
                               Title:  MANAGING DIRECTOR
                                      -----------------------------


                               PINKERTON NORTH ATLANTIC LIMITED


                               By:     /s/ James P. McCloskey
                                   --------------------------------
                               Title:   DIRECTOR
                                      -----------------------------


                               WKD PINKERTON SECURITY SERVICES GMBH & CO. KG

                               By PINKERTON'S GMBH
                               general partner

                               By:     /s/ James P. McCloskey
                                   ---------------------------------
                               Title:  MANAGING DIRECTOR
                                      ------------------------------
 
                               PINKERTON MANAGEMENT CORPORATION (for purposes of
                               Section 3 only) as a Subsidiary Guarantor

                               By:     /s/ Gary J. Hasenbank
                                    --------------------------------
                               Title:   VICE PRESIDENT
                                      ------------------------------

                               PINKERTON SERVICE CORPORATION (for purposes of
                               Section 3 only) as a Subsidiary Guarantor

                               By:    /s/ Gary J. Hasenbank
                                   -----------------------------
                               Title:  VICE PRESIDENT
                                      --------------------------


                               CITICORP USA., INC., AS A LENDER AND AS AGENT


                               By:      /s/ [illegible]
                                   ---------------------------------
                               Title:    ATTORNEY-IN-FACT
                                      ------------------------------

                               CITIBANK, N.A., AS ISSUING LENDER

                               By:    /s/ Marjorie Futornick
                                   ----------------------------------
                               Title:  VICE PRESIDENT
                                      -------------------------------

                               BANK OF MONTREAL, AS A LENDER


                               By:     /s/ [illegible]
                                   ---------------------------------
                               Title:  EXECUTIVE VICE PRESIDENT
                                      ------------------------------


                               DRESDNER BANK AG, AS A LENDER
                               New York and Grand Cayman Branches

                               By: /s/ Thomas J. Nadramia  /s/ Brigitte Sacin
                                   ------------------------------------------
                               Title:  VICE PRESIDENT  ASSISTANT TREASURER
                                      ---------------------------------------


                               PNC BANK, NATIONAL ASSOCIATION, AS A LENDER


                               By:    /s/ [illegible]
                                   -----------------------------
                               Title:  VICE PRESIDENT
                                      --------------------------


                               UNION BANK OF CALIFORNIA, N.A., AS A LENDER


                               By:    /s/ Linda L. Beaven
                                   ------------------------------
                               Title:  VICE PRESIDENT
                                      ---------------------------

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