Ever wonder how motion sensor lights and burglar alarms work? Take this quiz and learn how motion sensors and burglar alarms detect intruders.
It could be for either of two reasons: to let them know that someone has come in or to sound an alarm if someone leaves with unpaid goods.
The photosensor picks up the change in the light and immediately rings a bell.
The microwave energy is reflected back by a person and this causes the radar to respond by opening the door.
A motion sensor using ultrasonic sound waves bounces them off a target and detects the echo.
They're passive systems that are sensitive to body temperature; they don't actively emit anything.
They are usually sensitive to eight to 12 micrometers, bearing in mind that humans radiate infrared wavelengths of nine to 10 micrometers.
That's what makes it a motion sensor.
A motion sensing light has a lens that covers the sensor. Since infrared energy is a form of light, it can be bent with a plastic lens. The bent plastic lens is what offers a wide field of view.
Glass is not transparent to infrared energy, so it effectively blocks the sensor from picking up the infrared energy radiated by the burglar.
Sunlight streams through the glass, heating up the plants. The plants emit infrared energy, which is trapped beneath the glass because glass is opaque to infrared, causing the interior to heat up even more.