iPhone & Android have built in GPS as well as sensitive motion sensors.
Some of the apps use GPS only and can run in flight mode which means NO phone signal needed. You pre-load the Maps onto the device within the application so permitting signal free service.
http://www.guidingtech.com/31334/best-offline-maps/ Google also works in off-line mode but this requires some technical skills so if you are worried I would advise the off line maps tools which have the maps built into the App.
I don't mean that to provoke an argument, just to let people realise that it does not always need the signal like Google.
