Phaser sweep

A phaser sweep was a procedure in which a phaser emitter emitted a phaser burst that covers an area of a room. The procedure was introduced across the entire Starfleet in 2372 as a method to detect and stop Changeling infiltrators. On a setting of three or four, the Changeling reverts to it's gelatinous state, making it detectable. 

Aboard Federation starship's, all cargo and baggage brought aboard were to be subjected to phaser sweep's.