Cabin Crew are just taught that any little electronic devices held in your hand are 'bad' and must be stopped. There is no education about what is and is not acceptable. I have been stopped from using my little Pocket PC. Not a transmitter, but they do have Bluetooth and WiFi now which ARE! A little GPS looks like a mobile phone and could make someone else decide they will pull out theirs! So the only positive solution is to stop all use of such devices, which is sensible in your friend's case as handheld GPS doesn't work in aircraft cabins anyway- the antenna is shielded! (well mine didn't)