At first it was set to detect “pig anuses,” but the arrow always swung towards Washington DC. Then he recalibrated it for “random meat and minced ferret sphincters,” which seemed to work. Why a hotdog detector, you ask?

Because the bad robot was stealing Hot Dog stands. Buzz follows him, unaware he's about to step into a big pile of rotten produce.

See, the kid needs a hot-dog detector to detect the GIANT HOT DOG STAND in the sky clutched in the arms of a FLYING ROBOT. Otherwise you'd never notice.