If you need an alarm for your bike? then this is a simple – easy to build – transistor based motorcycle alarm could be suit with your need. This alarm will work at 12-volts but you can use 6 volt if you change the relay for 6-volt coil. It will protect your “Classic Bike” from thief. The standby current is virtually zero – so it won’t drain your battery.
Any number of normally-open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. While at least one switch remains closed – the siren will sound.
About one minute after all of the switches have been opened again – the alarm will reset. How long it takes to switch off depends on the characteristics of the actual parts you’ve used. You can adjust the time to suit your requirements by changing the value of C1 and/or R3.
The circuit is designed to use an electronic Siren drawing 300 to 400mA. It’s not usually a good idea to use the bike’s own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the Siren output – and use its contacts to sound the horn.
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