Smoke detector with external sampling volume and utilizing internally reflected light

1. A smoke detector comprising:

a housing;

disposed within the housing, a light source configured to (i) emit a first light portion outside of the housing and (ii) emit a second light portion within the housing substantially without emission therefrom;

disposed within the housing, one or more light detectors configured to receive light from the first light portion reflected back into the housing and light from the second light portion within the housing; and

an evaluation circuit for determining the presence of smoke particles outside the housing based at least in part on (i) at least one of a luminance or a rate of change of luminance of light received from the first light portion and (ii) a luminance of light received from the second light portion.

2. The smoke detector of claim 1 , wherein the housing defines an opening for emitting therethrough the first light portion and admitting therethrough light from the first light portion reflected back into the housing, the opening not having a window disposed therein.

3. The smoke detector of claim 2 , wherein light from the second light portion is reflected by a portion of the housing proximate the opening.

4. The smoke detector of claim 1 , wherein the housing comprises a window, substantially transparent to a wavelength of light emitted by the light source, for emitting therethrough the first light portion and admitting therethrough light from the first light portion reflected back into the housing.

5. The smoke detector of claim 4 , wherein light from the second light portion is reflected by the window.

6. The smoke detector of claim 1 , wherein the light source and the one or more light detectors are portions of a single electronic component.

7. The smoke detector of claim 6 , wherein the electronic component comprises a proximity sensor.

8. The smoke detector of claim 1 , wherein the light source and the one or more light detectors are not portions of a single electronic component.

9. The smoke detector of claim 1 , further comprising a gas sensor disposed at least partially within or on the housing.

10. The smoke detector of claim 9 , wherein the presence of smoke particles outside the housing is determined based in part on at least one of (i) a gas concentration sensed by the gas sensor or (ii) a temporal evolution of the gas concentration sensed by the gas sensor.

11. The smoke detector of claim 9 , wherein the gas sensor is configured to sense at least one of carbon monoxide or carbon dioxide.

12. The smoke detector of claim 1 , wherein the light source emits at least one of visible or infrared light.

13. The smoke detector of claim 1 , wherein the evaluation circuit is configured to determine the presence of a non-smoke physical obstruction outside the housing based on (i) at least one of a luminance or a rate of change of light received from the first light portion, and (ii) a luminance of light received from the second light portion.

14. The smoke detector of claim 1 , further comprising a manual test button disposed on the housing and electrically connected to the evaluation circuit, wherein, after actuation of the manual test button, the evaluation circuit performs a test sequence based at least in part on the luminance of the received first light portion and the luminance of the received second light portion.

15. The smoke detector of claim 1 , wherein (i) the light source comprises a broadband light source emitting light over a range of wavelengths, and (ii) the one or more light detectors comprise a plurality of light detectors each sensitive to light over only a portion of the range of wavelengths.

16. The smoke detector of claim 15 , wherein the broadband light source comprises a white light-emitting diode.

17. The smoke detector of claim 1 , wherein (i) the light source comprises a plurality of light emitters each emitting light of a different wavelength, and (ii) the first light portion comprises light at each of the different wavelengths.

18. The smoke detector of claim 17 , wherein the presence of smoke particles outside the housing is determined based in part on a difference between luminance of light received from the first light portion of a first wavelength and luminance of light received from the first light portion of a second wavelength different from the first wavelength.

19. The smoke detector of claim 1 , wherein the one or more light detectors comprise a plurality of light detectors each sensitive to light of a different wavelength.

20. The smoke detector of claim 1 , further comprising an ambient-light sensor, disposed at least partially within or on the housing, for sensing an ambient light level outside the housing.

21. The smoke detector of claim 20 , wherein the presence of smoke particles outside the housing is determined based in part on at least one of (i) an ambient light level sensed by the ambient-light sensor or (ii) a temporal evolution of the ambient light level sensed by the ambient-light sensor.

22. The smoke detector of claim 20 , wherein the ambient-light sensor senses at least one of visible or infrared light.

23. The smoke detector of claim 1 , further comprising a fault-detection circuit for automatically testing the smoke detector at least in part by comparing a signal generated by the light received by the one or more light detectors from the first light portion with a fault threshold derived from the luminance of the light received by the one or more light detectors from the second light portion, a fault being indicated if the signal generated by the light received by the one or more light detectors from the first light portion falls below the fault threshold.

24. The smoke detector of claim 1 , wherein the evaluation circuit utilizes, for determining the presence of smoke particles outside the housing, (i) a background signal derived from the luminance of the light received by the one or more light detectors from the second light portion, and (ii) a smoke threshold set higher than the background signal.