Picture of Remote Tripwire Alarm

A tripwire is one of the most basic ways to set up a simple security system. You run a line across a pathway. Then when someone walks through the line, it activates an alarm. This kind of system is easy to set up and is fairly effective. But there is always room for improvement.

The most inconvenient thing about a classic tripwire alarm is that it requires you to run a physical line from the tripwire to the alarm. This makes it difficult to set up a system where the alarm is far away or inside a building. To get around this problem, I designed a simple remote alarm system that uses a small radio transmitter to activate the alarm wirelessly. So in this project, I am going to show you how to make a simple remote tripwire alarm. 
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Step 1: Select a Wireless Transmitter/Reciever

Picture of Select a Wireless Transmitter/Reciever
The first thing that you need to do is select a small transmitter to activate the alarm. Just about any radio transmitter can work. I decided to use a wireless doorbell because it was small, battery powered and it is easy to program them so that multiple transmitters can activate one receiver. Some other examples of transmitters that can also work are things like walkie ralkies or garage door openers.

Step 2: Add Wires to the Switch on the Transmitter

Picture of Add Wires to the Switch on the Transmitter
The only modification that you need to make to the transmitter is to solder some extension wires to the button terminals so that it can be activated by an external switch. In most cases you will need to remove the circuit board from the housing in order to access the button terminals. 

Take two small piece of wire (at least three inches long) and strip the insulation off both ends. Then solder one wire to each side of the button. If your button has four terminals, you need to solder the wires to two terminals that are not connected when the button is not being pressed. You should use a multimeter to check which terminals are normally connected and which ones aren't.
cgrrty1 year ago
You can do that use two IR diode.

espdp21 year ago
Good Instructable. You may want to go back and show how you attached the transmitter to the clothespin, just for thoroughness' sake.
Better yet, you can place alarm bells, sirens, and flashing red floodlights everywhere throughout your building!
Another idea is to use a pressure sensitive mat some shops use.
TampaGeek1 year ago
Pretty cool... the only problem I have is that once the tripwire is tripped, the transmitter is going to keep transmitting isn't it?? I know you 'd need to go out and reset the wire itself, but there should be a way to have the transmitter stop after a certain amount of time (without running down the batteries).
mreamer1 year ago
Very cool idea! The board could be placed in an empty nuts/bolts/screw container to water proof it.
the clothespin switch idea is cool
nice work
Raphango1 year ago
Very cool indeed! While I was reading, a tougth came to my head: "Why don't upgrade it with a laser 'tripwire' for triggering the alarm system?" ;) This could make it even more top secret! =D