A Wired writer wanted to test just how effectively the Spot GPS Messenger could save his life. So, in the dark of night, he walked for 8 aimless hours into Tahoe National Forest. Then he pressed Spot's emergency button.
Having covered his tracks carefully and inserted himself as deeply into the forest as he could, it took only 30 minutes for a squad of rescuers, including snowmobiles, skiiers and a snowcat, to find him.
Every ten minutes, the Spot GPS device relays its location to 48 different satellites. You can have this data beamed to a website so friends and family can track your trek, but it's also available, when you hit the 911 button, to the GEOS International Emergency Response Center in Houston, Texas. When they receive the alert, they immediately determine the best rescue team and dispatch them to your exact location.
The Spot GPS is $169 with a $100 per year registration fee, but if you're adventure-inclined, it's probably worth it. [Wired]