dragnet

A dragnet is a basilisk-like reptile that has the ability to sniff out magic. It is used frequently at checkpoints by the Empyrean Empire, to sniff out portals other contraband.

Dragnet is a playful misinterpretation of dragnet:

drag·net /ˈdraɡˌnet/ noun a net drawn through a river or across ground to trap fish or game. a systematic search for someone or something, especially criminals or criminal activity. "many who had escaped the police dragnet retreated to a mountain hideout"