Smoke detector is for detection of fire & smoke, All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 9-35V DC.
It has been said that where there is smoke there is fire. It is even more true that where there is fire there is smoke. A fire sends little particles into the air. When these particles reach the smoke detector, they go through the little chamber where the electrons are flying from one electrode to the other. The smoke particles interfere with this flow enough to alert the microchip. The microchip is programmed to send a signal to the alarm.

Gas leak detectors can help you detect a LPG/natural gas/CO leak if you can't or don't notice its smell. When the gas reach to the alarm warning degree, the Gas detectors will make buzz sounds & lights to alert people.
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