When we hit the hill or the trail alone, we give ourselves and those at home greater piece of mind by attaching the Aleck Tocsen Helmet Crash Sensor to our helmet. This small, ultralight piece mounts to any helmet, has no running cost, and a long battery life for added safety that doesn't discriminate. When it detects a crash, it sets off an alarm that, if not responded to, will alert our emergency contacts, as well as emergency services within 1. 8 miles.