Use of GPS recievers by passengers
A friend who has a PPL was recently on a commercial flight and used a hand-held GPS receiver to monitor the progress of the flight. A member of the cabin crew asked him to switch it off as "it could interfere with the aircraft systems".
As he uses this in his own aircraft, he wondered what interference it could cause, as it is a receiver only and does not transmit any signal. He wonders how it can be safe to use in a Cessna 172 but not in a 737?
Over-zealous cabin crew? or am I missing something?