EXHIBIT 5









                                 March 14, 2006


Security Devices International Inc.
464 Old Orchard Grove
Toronto, Ontario
Canada M5M 2G4



This letter will constitute an opinion upon the legality of the sale by certain
selling shareholders of Security Devices, Inc., a Delaware corporation (the
"Company"), of up to 2,814,880 shares of common stock, all as referred to in the
Registration Statement on Form SB-2 filed by the Company with the Securities and
Exchange Commission.

We have examined the Articles of Incorporation, the Bylaws and the minutes of
the Board of Directors of the Company and the applicable laws of the State of
Delaware, and a copy of the Registration Statement. In our opinion, the Company
was authorized to issue the shares of stock mentioned above and such shares,
when sold, will represent fully paid and non-assessable shares of the Company's
common stock.

Very truly yours,

HART & TRINEN

William T. Hart