Mass of solutions already. Missed the boat on this one again. Some examples:
http://www.atmmarketplace.com/article.php?id=1451&na=1
http://www.atmmarketplace.com/article.php?id=52&na=1
Personally I like the dye-bomb solution. Just advertising the fact deters theft and the contents are useless to the thieves anyway. Much cheaper solution too than any monthly charged service.