Last year I went to Madrid in Vueling, I was sitted near the window with my yellow Garmin on my hand. I tried holding it against the window, locked enough satellites and then switched off the GPS.
One of the guys from the crew saw my GPS and gave me a 5 minute reprehension. I showed him that the device was off and said that the GPS only has a reception antenna (the signal is already there, I just catch it) and it would not interfere with the airplane. Still then, I listened "You would cause an airplane crash and kill everyboby!". The fun part was that everybody stared at me like if I had an yellow bomb.
It should be fun to see the speed, altitude and the route of the flight.
This entire post just to say that even an old yellow etrex can grab satellites if you hold it against the window.