Well this little ingenuity will allow you to not only trip someone but also have it set off an alarm when tripped. Its a fairly easy circuit to build and is incredibly straightforward. You shouldn't have any problems with this circuit at all, but if you do we're here to help.
For more similar projects, kits for this and other gadgets, and much more just go to Ocalon Electronics. If your having any problems with getting the circuit to work, or just general Q&A questions feel free to leave them here.
Step 1: Parts List
1. A single .01uF Capacitor
2. A 10K Resistor
3. LM555 Timer IC Chip
4. A SPDT Touch Switch
5. 9V Battery and Clip
6. Piezo Buzzer
7. Perf Board
8. About 8" of wire
9. 2 Position Terminal Block
10. An On/Off Switch
11. And a Project Case
Step 2: How Does it Work?
The touch sensor will be rigged so that when the lever is pushed shut, the power to the circuit will be turned off. Then once someone trips over the wire and it moves the circuit box it will allow the touch sensor's lever to open and then the circuit will turn on and set off the buzzer.
The switch is off by default and doesn't allow any voltage to flow to the 555 timer chip thus keeping the circuit turned off. But once the lever is open, the voltage is free to flow to the chip and turn it on. Once it does, the 555 timer turns into a simple audio oscillator which will drive the piezoelectric buzzer.
And that's all there is to the circuit. Its incredibly simple but very versatile. This simple configuration can be used in many a stealth and spy traps. This circuit's idea can be used to make an electronic trap that is triggered when someone passes by. Use your ingenuity to adapt this to your own uses.
Step 3: Building The Darn Thing
And if you need a more thorough walk through on what to connect to what, how to breadboard the circuit to make sure its working or just how to go about making the circuit then here's a link to the original project: Intruder Sentinel which has a step-by-step instruction set on what to do and how. If your having troubles or just wanna as a question then please do so! at our forum which should have a faster response time. =)
There are also project kits available for this and many other projects that you may be interested in!