Make a Simple and Safe Trip Wire Alarm to Catch Intruders

There are many ways to make trip wire devices, but the simplest way is to use a spring clothespin with contacts. A string or fishing filament can be used . Just secure one end of the line to something and the other end holds the contacts separated. When the string or line is tripped, the contacts are closed setting off the alarm. Any battery/relay combination can control any alarm from turning on a light to sounding a fire gong. The simpler the better.

And the clothespin solution doesn't consume power until tripped!

Hmm, I wonder if this ingenious spy tool has been declassified from the CIA files or is this another Wiki-Leak?

...and a simple IR device is invisible to human eyes and doesn't give itself away when you "cross" it as a "tugged" wire does (wink,wink).

Simple hacked camera phones are good IR detectors.

I'm just waiting for the "free energy" version to become available!