Abstract: A self-testable photoelectric smoke detector incorporates a housing which defines an internal smoke chamber. The housing carries a laser diode and a radiation sensor along with a supplemental source of test radiant energy. When a test is initiated, the operational characteristics of the laser diode are monitored simultaneously with energizing the source of test radiant energy. Signals from a scattered radiant energy sensor are evaluated via control circuitry, along with signals indicative of performance of the laser diode to determine whether or not the laser diode as well as the radiation sensor are functioning properly.