Proximity sensor
The proximity sensor was a sensor device that determined how close another object or lifeform was. The act performed with this device was a proximity scan.

Military uses 
The 22nd century Andorian scanner was equipped with a proximity sensor. In June of 2151, the Andorian Keval wasn't able to pinpoint the signal of the three new biosigns he detected so Thy'lek Shran told him to boost the proximity sensor. ()

Proximity sensors were commonly used on mines, where they trigger the mine's detonation when it nears or impacts a target. A malfunction in a proximity sensor could cause the mine either to detonate prematurely or to not detonate at all. (; )

Navigational uses 
A proximity alarm warned Cadet Jean Hajar of an impending collision with Cadet Joshua Albert's training craft, allowing herself and most of her Nova Squadron teammates who were flying in tight formation to initiate their emergency transporters before their starships were destroyed in the ensuing pileup. ()

Lieutenant Jadzia Dax had to repair the proximity systems on an abandoned, decrepit Bajoran raider hidden in an underground cavern so that she and Major Kira Nerys did not end up "bouncing off the walls". ()

See also 
 Proximity detector
Sensor technology
Weapon components