Photoelectric smoke detector and alarm system

Claim 1

In a smoke detector and alarm system, the combination including housing means defining a light tight interior chamber, said housing means having an inlet opening and an outlet opening each communicating with said interior chamber, means in said housing means including a plurality of baffles defining a tortuous passageway preventing the passage of ambient light into said interior chamber while permitting air and airborne particulate matter contained therein to flow into said interior chamber from said inlet opening and out of said interior chamber through said outlet opening, piezoceramic electrically activatable alarm means carried by said housing means, an illuminating circuit including a gallium aluminum arsenide light emitting diode mounted in said interior chamber, means providing a direct current supply for said light emitting diode, a smoke sensing circuit including dual photoelectric means formed on the same substrate and the electrical conductivity of each of which varies as a function of the amount of light impinging thereon, said dual photoelectric means being connected in series and being electrically connected to said means providing a direct current supply for said light emitting diode, means mounting said dual photoelectric means in said interior chamber in proximity to said light emitting diode whereby light emanating from said light emitting diode impinges upon one of said dual photoelectric means at all times and impinges upon the other of said dual photoelectric means to change the conductivity of said dual photoelectric means when airborne particulate matter is present in said interior chamber, and means activatable in response to a differential in the conductivity of said dual photoelectric means for activating said piezoceramic alarm means.