A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.
A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation, and looks for changes in the field or return signal.
The object being sensed is often referred to as the proximity sensor's target.
Proximity sensors are commonly used on smartphones to detect accidental touchscreen taps when held to the ear during a call.
They are also used in machine vibration monitoring to measure the variation in distance between a shaft and its support bearing.
A proximity sensor adjusted to a very short range is often used as a touch switch.