What is the purpose of a proximity sensor in a smartphone?

The purpose of a proximity sensor in a smartphone is primarily to detect when the device is in close proximity to an object, typically the user's head during a phone call. This functionality is crucial because when the phone is brought close to the face, the proximity sensor can detect this and automatically turn off the display. This helps to prevent accidental touch inputs on the screen while the phone is held to the ear, which could result in unintended actions such as dialing other numbers or muting the call.

This feature enhances user experience by ensuring that the phone operates efficiently during calls, allowing for a clearer focus on the conversation without interference from the screen lighting up or receiving accidental inputs. The other options, while related to phone functionalities, do not pertain to the specific role of the proximity sensor in managing display behavior during close contact scenarios.