burglar deterrent

elektor july/august 1985 L. __ — —.J Most burglar deterrent systems are based on the same principle: once the presence of an unwanted or sus- picious individual has been detected (by electronic or other means), some action ensues which makes it clear to passers-by or neighbours that something is amiss. It is often overlooked that the unwanted visitor first had to ascertain that there is nobody at home. The majority of burglars who operate by daylight just ring the bell. Once they have repeatedly rung without anyone answering the door, they go about their nefarious ways. Once inside, they may well set off a conventional alarm, but by then it is already too late. The circuit proposed here was designed to prevent the intruder getting that far. When the bell is rung, a number of monostables is actuated, which, after a suitable delay, switches on a cassette player that generates an awesome sound. This can vary from the barking of a large dog to the roar of a lion, depending on the ...