While PIR sensors can be used with Arduino and other microcontroller boards, those best-suited for hobby use are smart enough to perform simple tasks without any programming.

There's really not much to the motion sensor. The sensor shoots out an invisible light field that spans 100 degrees horizontally and 100 degrees vertically. Its blind spot is 180-degrees to its sides.

Philips uses the ambient light sensor too: you can set it so the lights won't come on if it's already bright, for instance, and the daylight sensitivity is adjustable.

HomeKit motion sensors are a vital accessory when building a smart home than runs by itself without manually turning devices on and off.

The iPhone utilizes a sophisticated set of sensors for many of its operations, from automatically adjusting screen brightness based on the light around you, to detecting motion for various apps ...