A sensor is a device that detects and responds to changes in its environment. Sensors notice things like temperature, light, movement, or sound, then send that information to a computer or control system that can use it.

You interact with sensors constantly. When you walk through a door at the grocery store and it opens automatically, a motion sensor detected you. When a smoke detector goes off during a cooking mishap, its sensor noticed particles in the air. Your phone's screen brightens in sunlight and dims in darkness because a light sensor adjusts it automatically.

Sensors work like artificial senses: they're the eyes, ears, and skin of machines. A car's parking sensor acts like a sense of touch, beeping faster as you get closer to an obstacle. A thermostat uses a temperature sensor to know when to turn the heat on or off. Video game controllers have motion sensors that detect how you tilt and move them.

Modern life depends on sensors everywhere. They help pilots fly planes safely, let scientists study earthquakes, and even allow your fitness tracker to count your steps. Without sensors feeding information to computers and machines, much of today's technology simply wouldn't work. A sensor is what allows a machine to notice what's happening around it and respond appropriately.