I don't think this would help me in a drain
I always tell my wife where I will be and use google lattitude so she can track me, if I don't call back at a set time she knows I'm dead
pretty much the same as if your going hill walking leave a route you will take and don't deviate or by much. i usually tell a few people. Take it you have gps on latitude as we used it when things go pear shape to find each other but it sometimes gets a bit flaky