Here is a nifty article on using the 22 caliber power cartridges for nail guns to make a perimeter alarm. They are also available on Ebay according to the article. Be sure to follow all safety precautions and don't set the dry woods on fire with one of these... Jim
http://www.gunsamerica.com/blog/prepping-101-perimeter-alarm/
http://www.gunsamerica.com/blog/prepping-101-perimeter-alarm/