The Barnacle is a replacement for the Denver Boot (that wheel-hugging device used to immobilize a car that's racked up too many parking tickets). The Barnacle attaches to the car's windshield by suction, creating an opaque barrier. It automatically releases when the driver pays the fine on the phone or online. It's safer for parking enforcement officers, because they don't have to squat down in traffic to attach it.
Some people will stick the head out of the driver's side window and drive away. They can do that, but an alarm will go off and a built-in GPS tracker will know where they are.
[via]
