A self-contained smoke detector system has internal self-diagnostic capabilities and accepts a replacement smoke intake canopy (14) without a need for recalibration. The system includes a microprocessor-based self-diagnostic circuit (200) that periodically checks sensitivity of the optical sensor electronics...http://www.google.com/patents/US5936533?utm_source=gb-gplus-sharePatent US5936533 - Method of automatic verification of smoke detector operation within calibration limits
