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Door Knock Beeper -- June 14, 2009

2014-11-03 19:02  
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Door Knock Beeper -- June 14, 2009
In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door. The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door from the outside. The circuit is powered by a 9v battery, which should provide years of service. An on/off switch allows the device to be turned off if desired. It is suggested that the circuit be housed in a plastic box with a 9v battery holder. A Serpac box from Mouser, part number 635-211-I-G is just right for this application. It is about 4 inches long and 2.6 inches wide. It has a nice compartment for a 9v battery. Source: discovercircuits