Patent ID: 8907802

Claim:
A method of smoke detection utilizing a smoke detector comprising (a) a housing, (b) one or more light emitters, and (c) one or more light detectors, the method comprising: at a first time, acquiring a first measurement of light including a first wavelength originating outside the housing without emitting light of approximately the first wavelength from the one or more light emitters; at a second time later than the first time, acquiring a second measurement of light including the first wavelength originating outside the housing while emitting light of approximately the first wavelength with at least one said light emitter; at a third time later than the second time, acquiring a third measurement of light including the first wavelength originating outside the housing without emitting light of approximately the first wavelength from the one or more light emitters; at a fourth time, acquiring a first measurement of light including a second wavelength originating outside the housing without emitting light of approximately the second wavelength from the one or more light emitters, wherein the second wavelength is longer than the first wavelength; at a fifth time later than the fourth time, acquiring a second measurement of light including the second wavelength originating outside the housing while emitting light of approximately the second wavelength with at least one said light emitter; at a sixth time later than the fifth time, acquiring a third measurement of light including the second wavelength originating outside the housing without emitting light of approximately the second wavelength from the one or more light emitters; detecting an ambient light level outside of the housing; correcting the second measurement of light including the first wavelength based on (i) the detected ambient light level and (ii) at least one of the first or third measurements of light including the first wavelength, thereby producing a corrected first-wavelength measurement; correcting the second measurement of light including the second wavelength based on (i) the detected ambient light level and (ii) at least one of the first or third measurements of light including the second wavelength, thereby producing a corrected second-wavelength measurement; and determining the presence of smoke particles outside the housing based on a ratio of the corrected first-wavelength measurement to the corrected second-wavelength measurement.