Scanner

The Scanner was a gadget that was used by Batman to help him to detect spores of the plant that was required to make the antidote for the Titan Formula. Unlike the other gadgets, the Scanner couldn't be selected and was only seen in Batman: Arkham Asylum.

Arkham Asylum Incident
Batman used the Scanner to help him to detect spores that used to make antidote to the Titan Formula in Killer Croc's Lair, but Croc appeared to try to kill Batman. After Croc was defeated, the Scanner was not seen until the end of the Incident.

Trivia

 * That was the only gadget that Batman used that the player couldn't control.