The Battle Scanner Provides extra vision on the battlefield. Soldiers deploy it like a grenade, throwing it to a hidden area of the map that they want to reveal. Any hidden or disguised enemies will be revealed as well.
Battle Scanners only take a single action point to throw, and do not end the turn. This means you can use both of them in a single turn to scout a large area of the map at once, or perhaps throw one at a known Chryssalid location to remove it from burrow, and then follow up with a shot.