Sensor (noun)

1. A device that detects or measures a physical property and records, indicates, or otherwise responds to it.
2. An electronic device that detects or responds to a physical stimulus such as light, heat, motion, moisture, pressure, or magnetic fields.
3. An electronic device, typically with a small screen, that can be carried on the person and used to record and store data such as distance traveled, heart rate, and calories burned.

Origin:

Early 19th century: from latin sensus "feeling, perception", from sentire "to feel", based on the latin word sensus "feeling, perception", from sentire "to feel".

Examples:

1. A sensor on the car's engine indicated a problem.
2. The camera has a light sensor.
3. The burglar alarm is triggered by a motion sensor.
4. The smartwatch has a heart rate sensor.
5. The irrigation system has a moisture sensor.