An Arduino can be the starting point for replacing many consumer items, and one of these is an alarm system. With many inputs and outputs connecting various sensors and alarms is simple, and one interesting example of this has been documented by Ronnie Tucker.
His system uses a laser trip wire as a main detector - the Arduino monitor the status of a light sensor with the laser pointing towards it - when the line is broken, the alarm can be sounded. Furthermore, the system is activated or deactivated via a password or PIN entered with a numeric keypad. An example of operation is shown in the following video:
This is also a great way of learning how to use numeric keypads with Arduino - which opens up all sorts of user-input options. For more infromation about this project, visit Ronnie's Instructable page. And for more, we're on twitter, facebook and Google+, so follow us for news and product updates as well.
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Our tiny light-sensor module uses the very-reliable TEMT6000 light sensor, which gives consistent and repeatable readings even between different units - unlike cheapie light-dependent resistors, which can vary dramatically in their sensitivity. So for reliable light sensing - look no further.