[LETTERHEAD OF WILSON SONSINI GOODRICH & ROSATI]

                                                                     Exhibit 5.1

                                  April 1, 2002

Sierra Monitor Corporation
1991 Tarob Court
Milpitas, California 95035

     Re: Registration Statement on Form S-8

Ladies and Gentlemen:

     We have  acted as  counsel  to Sierra  Monitor  Corporation,  a  California
Corporation  (the  "Registrant"  or "you") and have  examined  the  Registration
Statement on Form S-8 to be filed with the Securities and Exchange Commission on
or about April 2, 2002 (the  "Registration  Statement")  in connection  with the
registration  under the Securities Act of 1933, as amended (the "1933 Act"),  of
1,000,000 additional shares of your common stock reserved for issuance under the
1996 Stock Plan (the  "Plan").  As your legal  counsel,  we reviewed the actions
taken and proposed to be taken by you in  connection  with the proposed sale and
issuance of the shares to be issued under the Plan.

     It is our opinion that,  when issued and sold in the manner  referred to in
the  Plan and  pursuant  to the  agreements  which  accompany  the Plan and upon
completion  of the  actions  contemplated  to be taken in order to  permit  such
transactions  to be carried out in accordance  with the  securities  laws of the
various states where  required,  the shares will be legally and validly  issued,
fully paid and nonassessable.

     We  consent to the use of this  opinion  as an exhibit to the  Registration
Statement and further  consent to the use of our name wherever  appearing in the
registration statement, and any amendments thereto.

                                    Very truly yours,

                                    /s/ Wilson Sonsini Goodrich & Rosati
                                    --------------------------------------------

                                    WILSON SONSINI GOODRICH & ROSATI
                                    Professional Corporation