Patent ID: 7834773

Claim:
A smoke detector, comprising: an optical case having an inner portion constituting a black box; an air passage which constitutes a smoke detection portion by allowing a gas to flow into the optical case; a light emitting element disposed in the optical case; a light receiving element for receiving scattered light generated by scattering light emitted from the light emitting element by smoke particles existing in the smoke detection portion; a light trap opposed to the light emitting element, for attenuating stray light; a condenser lens for condensing the light emitted from the light emitting element in the vicinity of the light trap; a received light amplifier circuit for amplifying an output signal of the light receiving element; and a fire determination portion for determining fire when a detection level obtained by A/D-converting the amplified output signal is equal to or larger than a threshold value, wherein the light trap has a curved surface portion having a substantially conical shape and the curved surface portion reflects the stray light a plurality of times and attenuates the stray light, the incident angle θ of the stray light with respect to a tangent line of the curved surface being equal to 45° or less.