The tripwire alarm produced by Ice Bear Alarm in the UK is the best engineered alarm we have come across. Some alarms rely on batteries (which may go flat) or buzzers (which you can sleep through) while any system that relies on electronics is vulnerable to damp and short circuiting. When it comes to alarms simplicity equates to reliability.
The alarm is designed to use standard 12g blank cartridges. Black powder cartridges will give the loudest bang but other 12g blanks will also work. Alarms are usually set with four alarms around the camp using corner posts and fine, strong, non stretching fishing line as a tripwire. If anything passes through the line, it triggers the device and fires the cartridge downwards. This produces an instantaneous and very loud bang, close to the ground and to the intruder. Apart from warning you that an intruder has entered the perimeter, it can often scare off the offender.
We strongly recommend this alarm because it is simple, self-contained and easy to reload with a fresh cartridge. It can be attached to posts using screws, wire, string, tape or cable-ties.
Although the Ice Bear Alarm was originally designed for use in severe arctic conditions, it can be used wherever unwelcome visitors may be present. Grizzly bears, Brown bears and other animals can pose a threat to the security of camps or personal property.