Is a GPS purely passive? To prevent a terrorist from using a civilian GPS for a targeting computer, it seems that there must be some ability to "see" a GPS by military types... and i suspect that it is secret, but that there already is a way to locate a GPS on the ground.

That said, you can always read your GPS coordinates to the 911 operator... the idea is really to join the two functions, and i don't see the advantage. The cell phone already has a location register for which receiving cell it is in... and this already is a tremendously effective locator... for the lost/rescue sense.

That said, it seems you hit on the mobile phone as an emergency device... and in this regard, i keep a prepaid one in the car glove box... It would be nice if that phone had special emergency features at buttonpress.. one press for Rape/violent crime in progress, one press for come and get me lost, one for car breakdown... it seems only logical to better tune the "mobile" to become a pure emergency phone... waterproof with battery-extra just in case.. maybe with a radio-frequency beacon built in to it for homing in as you describe... a GPS might be less preferable to a transmitter of some sort that could flash radio-waves for an hour that a crew wandering in the dark could locate you.

Good idea, just is the GPS all that necessary.

The cellphone industry has already been mandated by the Feds to have GPS working on all cellphones whithin the next couple of years. They will just use triangulation until they get their GPS system set up. If you don't want to be found, you just turn off your phone.