Intruder Sentinel


Introduction: Intruder Sentinel

Tired of always being snuck up upon? Doing any stealth surveillance or reconnaissance? Or maybe you just need to set-up a fail-safe alarm for your stuff so your little brother doesn't go into your room.

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

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

Preferably: (Optional)
9. 2 Position Terminal Block
10. An On/Off Switch
11. And a Project Case

Step 2: How Does It Work?

The entire project functions as a switch triggered alarm which we are using as our intruder detector. The circuit works by having the touch sensor operate as a switch which turns the power to the circuit on and off.

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

Okay so now you have the schematic which is pretty much all you need to get started building this project. But for those of you who may be having trouble figuring out what goes where and "what is this dookickey do?" or "where can I get this whatchamacallit?" then just go here and hopefully you'll find what you're looking for. If not then just post a message and let us know.

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!



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    22 Discussions

    Its Better to use Laser Than Switch use LDR Or InFrared For Receiver of the Laser

    i tried making it and this doesnt work. I made a better circuit, a double oscillating blinkie light so when one is on the other is off, like those yellow traffic things.

    1 reply

    this is a sensor...why need to use SPDT switch?...are you saying that we have to trigger the switch so that it can detect?...maybe its nice to use laser or photo transistor rather than a switch.

    this is a sensor...why need to use SPDT switch?...are you saying that we have to trigger the switch so that it can detect?...maybe its nice to use laser or photo transistor rather than a switch.

    Did you actually build this?
    The screen-shot step 3 is particularly lazy (PocketSized's comment noted also.


    2 replies

    Yeah, that's just a screenshot of the steps. I haven't gotten around to posting the step-by-step instructions yet. I'll try and get on that.

    It would be good to see them - something you've yet to build? or is it just putting the instructions together? L

    The schematics for this project are scanned straight from the pages of
    101 Spy Gadgets for the Evil Genius (With slight modification). Yet you didn't feel it worth giving the guy credit?
    No link, not even a brief mention?

    While part of the Instructables community thrives on the well documented reproduction of projects. It does not appreciate other peoples ideas/projects being stolen soo blatantly without even a mention of the original creator...

    This is without taking into account the copyright implications of scanning in the original owners schematic.
    While it could be argued that the circuit is soo simple anyone could have coincidentally come up with it, this doesn't account for the identical schematic.
    Which shows there is no coincidence, coupled with the fact you didn't even feel the author of the circuit deserved a quick mention.

    I have added a photo of the original circuit graphic, just as proof.
    However because I value the original authors' work I will remove it shortly.

    1 reply

    You're absolutely correct! I did have an image caption about how this project is a variation of the one built by Brad Graham. I'm not sure what happened to it. But I have updated the image so the caption is included in it. Thanks for the reminder =)

    Could I build it? I know the bare minimum about electronics, but I could probably follow the instructions depending on if it is suitable for novices.

    5 replies

    Yeah, this is a pretty basic circuit so you shouldn't have any problems, but if you do just let us know or post it to our forum and we can help you out.

    looks simple enough for a novice, if u can solder. just dont allow the components to get too hot while soldering ;) (allow time to cool between soldering pins and legs ;) ) if soldering tutorials are needed there are plenty here on instructabubbles.

    Chips, like a 555, contain semiconductors very sensitive to static electricity and to heat. It might be safer to spend a very little extra and get a socket for the 555. After it is soldered, insert the chip. A socket could make life easier, especially for a novice.

    Sockets are definitely a great idea because you can take the chip in and out whenever you need to. That way you can switch out a broken chip for a new one or use that same chip later on if you decide to scrap the circuit.