This is an alarm system that works with a percussiona cap.
(sorry about my bizarre english)

Hi. I'm a professional magician/illusionist (despite the common sense, it´s the same thing) from Brazil, writer of a book called "Imagica", about magic Theory and Psichology and want to say something:
Most of magicians don´t like Blaine and Angel style and way of amazing people. They are good sometimes, but most of time, they sucks. When a magician needs fake bystanders or/and camera, special efects or post-edition manipulation of images, he isn´t doing the truly MAGIC ART. Magic is a Art and this guys aren´t good artists.