Burglar and fire alarm for door - uses two insulated metal foils attached to either side of door which trigger alarm if connected by any metal object used to cut through them

摘要

The burglar or fire alarm system protects a doorway. The door is covered by two thin sheets of metal foil separated by a thin layer of insulating material. The two sheets are connected in series in acircuit which includes a battery and sound and light warning devices. If an attempt is made to break through the door using any metal object, the two foils become connected and the alarm is sounded. The foils may be covered by a decorative finish, on the outside, and may be glued to the door itself.