"The pamphlet-makers were still clustered around the remains of the Decoy Detonator, which continued to hoot feebly as it smoked. Harry hurried off up the corridor as the young witch said, 'I bet it sneaked up here from Experimental Charms, they're so careless, remember that poisonous duck?'"
A Weasleys’ Wizard Wheezes product used for creating diversions.
This Weasleys' Wizard Wheezes product is a "weird-looking black hooter-type object" that, when dropped, will scurry off and make a loud noise just out of sight. Even when not in use, a Decoy Detonator will attempt to do this, though without setting off a noise (HBP6).