Boo Radar

The Boo Radar is a feature on the Game Boy Horror. During the events of Luigi's Mansion, after Luigi accidentally let free all of the Boo's in the mansion, E. Gadd showed him the Boo Radar. If the light is blue, there are no Boo's in the room. If it is yellow, there is a Boo in the room (or just something round, like a ball or a bomb). If the light is red, a boo or something round is right in front of Luigi, and he would use his Poltergust 3000 to suck it up.