How do I make a system where it sends me an alert when a wire is cut?

I work for a non-profit in Mexico. We have a remote station with an antenna and computer equipment that I need to secure from people messing with the antenna on top (people taking it for metal recycling money is my main concern). I plan on putting a line or two of barbed wire lining the top of the building that houses the computer equipment inside.

However, because it's so remote from where we are generally (it's on top of a hill next to us), I need some kind of remote alert system so that I know if the barbed wire has been cut.

I saw a garage door monitor instructable using the parallax "Basic Stamp II" that I think I could modify for this purpose, but I figured this has been done before and their is probably a better way to do it.

I thought of several ways to detect that the wire was cut, like running a small current through it so that when the circuit is broken, it sends the alert (e-mail or something like that), but I don't know how to implement that.

It should be noted that the barbed wire is going to be on top of a 4 ft x 4ft building. There are no gates involved and it is a continuous wire (total 16ft long). I need to have a system that will tell me if any of the four sides gets cut.

I've included a basic layout to help visualize what I'm talking about.

Thanks for the help everyone. This is an awesome website.

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orksecurity7 years ago
You're exactly right on the wire detection. Same as a home alarm system -- when the circuit opens, it releases a relay (or equivalent), which closes a connection, which causes the alarm (of whatever kind).

In fact, simply buying an off-the-shelf alarm system with an autodialer or (better) a monitoring service will do the job. If this is something you've got money riding on, there's something to be said for buying a system, particularly if it's one that comes with some kind of insurance program. (Good luck finding one of the latter in Mexico, but ya never know.)

Note that for this to work, you will have to insulate the barbed wire from the fence. Note too that you're going to have to figure out what to do about the gates.

grundisimo6 years ago
could you turn the metal (barbed wire) into an electric fence?
I think what ork is suggesting is just that you replace the OTS alarm system's sensor with a loop of barbed wire. In the regular setup, the sensor is just a switch or a contact point that tells the alarm controller when the circuit is broken. If you wire the leads from an alarm controller to each end of your loop of barbed wire, the wire itself will act as the switch. If the wire is cut, or the circuit is compromised in some other way (i.e. someone leaning a metal ladder against the wires, causing a short, the alarm will activate. The only trick is making sure that the barbed wire is insulated from the supports and the other strands of barbed wire.
Whoops, this was supposed to be attached to orksecurity's thread.
How are you going to get the alarm signal back to where you can do something with it ? 
a mechanical solution