I really don't know the reason for the flyaways. One was with a Vision, I was flying at about 150 m from Home, suddenly it started off in quite another direction, and was uncontrollable - just carried on, on the track to China or wherever. The battery was full, so it could have gone quite far.
The other was similar (Phantom1), but I could hear it behind some trees, until it the engine sound died away, the quad also unresponsive to every attempt of control (I could see what the Gopro saw on my monitor, so it probably were only a few hundred meters away, in dense bushes) - but a search afterwards in the pinpointed area didn't recover it. It was equipped with a GPS-tracker, bearing the fate of the Vision in mind - but apparently the tracker was out of phone coverage, anyway it didn't respond to me calling it, no texts came back.
So I lost quad and tracker (and Gopro).
For some time, I lost everything I may have had for DJI and didn't want to hear anything Phantom - but nevertheless, 6 months later, I find myself in a possession of a Phantom 2 - that I don't want to lose.
A loud, audible alarm would probably have located the second one lost, and the beacon suggested previously in the thread may have had located both of them.