At least on UK networks you get an indication that says 'emergency calls only' when you are within range of any network.

Does a similar thing happen in the US?

Also seems like a perfect application for those Stingrays the police have stockpiled.

I'm not aware of a similar thing in the US. And depending on the remoteness of your location, you may get an indication of a good signal (3+ bars) but still be unable to transmit or receive a text. It's common in the mountains where I hike and backpack to get "ghost bars" like that which suggest you should be able to send and receive messages but only a tiny percentage ever get through, if any.

The US has actually several emergency networks, a cellphone even without a valid sim card can still be used to dial 911 this is part of every cellular standard. But in more common cases when you are outside of the coverage of your carrier and with roaming disabled/no roaming partners you will still see Emergency/SOS displayed on your phone.

http://s9.postimg.org/umb1a3tjz/s5570.jpg

Besides 911 there are probably a few other emergency numbers in the US which are open on all cellphones, as well as the emergency broadcast system which will display push notifications on every modern cellphone in such cases as natural disasters.

Assuming the phone uses the same standard (ie. GSM vs. CDMA), this is true here in the US.

LTE, however, is making this less of an issue and in theory an LTE capable phone should be able to make an emergency call from any network.

Interesting. I wonder if these would have been used if the lost person was rich or famous.

Starfish

Erm. Wrong codename. Stingray.

Government surveillance already has multi-band and protocol mobile tower stand-ins.