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A proximity sensor is an electronic sensor that can detect the presence of objects within its vicinity without any actual physical contact. In order to sense objects, the proximity sensor radiates or emits a beam of electromagnetic radiation, usually in the form of infrared light, and senses the reflection in order to determine the object's proximity or distance from the sensor.
Proximity sensors are commonly used in industrial applications, from manufacturing and food production to recycling. They are also used in vehicles for detecting the proximity of other vehicles relative to one's own car, as well as for parking-assist functions. In mobile devices, especially phones, the proximity sensor is used to detect whether the user's face is close to the phone during a phone call, prompting the screen to turn off to prevent false touches on the touchscreen.
There are many types of proximity sensors and they use different methods for sensing. For example, capacitive and photoelectric sensors are more suited to plastic and organic targets, whereas inductive proximity sensors can only detect metal targets.
Below are some of the types of proximity sensors: