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A very simple and light, answer to bike thieves. :

www.youtube.com/watch?v=CbogMB2wCm4

Lets see how to put it together:

Step 1: Material List and Schematic

This is the schematic.

As you can see the materials needed are:

1 On/Off switch, (preferably a round key switch witch can fit in the handlebar end of your bike.
1 mercury switch
1 2.5K resistor
1 10K resistor
1 4.7μF capacitor
1 BD139 transistor, (although any NPN transistor will fit)

Also - (not shown here), 1 12V battery, (the ones used in car alarm transmitters)
 

Step 2: The Final Assembly

In these pictures you can see the battery used as well as the switch used. The switch has been mounted inside the tap of the handlebar. I've make the battery holder out of an old flashlight.

Step 3: Mounting

As you can see in the video in step 1, i've put the sireen inside the left end-bar grip and the wires pass under the tape and inside the tube where it meets the circuit.

Thats all!

Good luck and enjoy.
Do you have a parts list of where all of those parts are available? <br> <br>I'm specifically looking for that mercury switch. Thanks. <br>
Quality! If installed correctly, then no one would see this at all! Would love to see a video of it in action. Does the alarm keep ringing or does it stop if the thief puts the bike back?

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