Sneakoscope

A Sneakoscope is a Dark Detector shaped like a glass spinning top. When somebody untrustworthy is up to something nearby, it lights up, spins and whistles. Edgar Stroulger invented it in the eighteenth century. Cheap pocket models are sold to tourists and have a poor reputation, since they go off at the least provocation and are widely written off as rubbish, though a Sneakoscope shrieking for no visible reason has sometimes simply noticed something its owner has not. Larger models run to the other extreme, sensitive enough to pick up deceit a mile away, which makes them useless anywhere near a school full of students fibbing about their homework.