A look inside a photoelectric smoke detector that uses infrared light to detect an increasing smoke level in a room.
I strongly recommend buying smoke detectors from local outlets like supermarkets, as that will guarantee a device that is compliant with your countries regulations.
There are very poor quality smoke detectors on eBay that use a cheap microcontroller to give basic functionality (if they even work at all) but for just a little more you can get real branded units.
I think this one either came from Poundland or the local Shoprite (Isle of Man) where they cost around £5.
This one uses a dedicated chip that is designed to self test in several ways, and also reduce the risk of false alarms by differentiating between specs of dust passing through the sensor and actual smoke.
The sounder is driven by a dedicated section of the chip with proper feedback to ensure it is loud by resonating at its maximum efficiency.
The shielded infrared smoke detection chamber has an emitter and sensor positioned to avoid direct light coupling. But the circuit does test the emitter and detector by looking for the low level coupling that occurs by reflection.
I recommend replacing smoke detectors at least every ten years. They can accumulate dust and reduce in sensitivity over time. They cost so little that it can be considered preventative maintenance. If you buy the same type it may fit on the existing base for an easy swap.
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