Climbing Mt. Everest? The accelerometer in this rescue beacon detects the subtle movements that indicate you're still breathing, and the device radios your health status and location to rescuers. $400; mammutusa.com
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.