Radio jammer. Civilian models go into "safe mode" and cease forward motion, descending slowly until signal is regained or they hit the ground. Don't really know much about military models though.
Saw a guy at the river flying one, his smart phone docked into the remote and became the live view screen, if it flies out of range, satellites bring it home, pretty cool toy. Crash it? 1,000 dollar toy.
‘There is no God but Resister and Refugee is his messenger’.