The Ultimate Motion Sensor and Burglar Alarm Quiz

By: Staff
Image: refer to hsw

About This Quiz

Ever wonder how motion sensor lights and burglar alarms work? Take this quiz and learn how motion sensors and burglar alarms detect intruders.

Why do they have those electronic devices at store entrances?

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.

A photosensor works by facing a beam of light. When someone walks through and breaks the beam:

The photosensor picks up the change in the light and immediately rings a bell.

An automatic door opener that uses radar sends out a burst of microwave radio energy. How does this make the door open?

The microwave energy is reflected back by a person and this causes the radar to respond by opening the door.

How does a motion sensor using ultrasonic sound waves work?

A motion sensor using ultrasonic sound waves bounces them off a target and detects the echo.

Are motion sensors that detect infrared energy active or passive systems?

They're passive systems that are sensitive to body temperature; they don't actively emit anything.

What is the range of sensitivity of infrared sensors?

They are usually sensitive to eight to 12 micrometers, bearing in mind that humans radiate infrared wavelengths of nine to 10 micrometers.

Why does a motion sensor detect only rapid change, such as a person walking?

That's what makes it a motion sensor.

How does a motion sensing light have a wide field of view?

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.

Why can't a motion-sensing burglar alarm detect a burglar outside your window staring at you?

Glass is not transparent to infrared energy, so it effectively blocks the sensor from picking up the infrared energy radiated by the burglar.

What does infrared energy have to do with greenhouses?

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.

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