Baffle callers to your home with this low-cost, delayed action versatile alarm

From time-to-time, the author has placed electronic designs in the public domain. Recently he sought to find out which of these, over the years, had been the most popular, based on the quantity of mail received. It came as something of a surprise to him that this was a simple Gate Alarm.

This emitted a pip-pip-pip tone when a person entered the front gate. It was intended not so much as an alarm, as to give the impression, “You have been noticed”. The design presented here is a de-luxe version of the original – yet it remains very simple. Its chief characteristic is that the tone it emits is set apart from the action of the gate. Thus the perception is that the alarm has not been triggered by the gate. In fact during testing, people tended to look around to see how they might have been detected – not suspecting that the alarm was connected to the gate.