Recommended by the Mountain Leader Training Board as an essential item to be carried in the hills.
The international distress signal is 6 blasts of a whistle every minute.
The recognised reply is 3 blasts every minute. (TIP if you are calling for assistance and hear a reply, KEEP blowing the signal until rescue appears in sight, otherwise your rescuers will not be able to find you if you stop too early!)
100 decibels loud Lightweight Durable No Moving Parts