How Does a Motion Sensor Detect Movement?

A motion sensor detects movement and triggers an electronic action.

Motion sensors are used in many household and commercial products. They detect movement through infrared or sound waves or through an accelerometer. Then they trigger an electronic response, such as turning on a light, opening a door, starting an alarm, or causing a movement in a video game.

Infrared Waves

Infrared motion detectors use infrared waves, which are just longer than visible light waves. They cannot be seen by a human eye, but every object that generates heat generates infrared waves. Motion sensors detect changes in the amount of IR waves, which triggers an electronic response. Window and door residential burglar alarms use IR waves. These are known as passive sensors.

Sound Waves

Other motion detectors are sound-wave based. These types of detectors may also use microwaves. The device is constantly emitting waves. As long as they bounce back in the expected pattern, the device remains passive. When the waves are disturbed, the device triggers an action such as opening an automatic door. Interior burglar alarms, such as those found in museums, use sound wave technology. These are called active motion detectors.

Accelerometers

Motion-sensing video games use a different type of technology called an accelerometer. These are computer chips attached to a controller or a hand-held device such as a smart phone. The chip detects the capacitance, or ability to retain an electric charge, at different places on the chip. With accurate measurements of where and when the wafer moves, the video game or electronic device can accurately recreate that movement on screen. Accelerometers were first developed for the Defense Department to guide missiles and were expensive and large. Now they are as small as a penny and more affordable.

References

• Glolab: How Infrared Motion Sensors Work
• Science Line: How Do Motion-Sensing Video Game Controllers Work?
• Softpedia: How Motion Sensors Work