copy/paste from a prior post of mine:
OK so, right now in Phantom mode the 2 control switches on your remote don't do anything (during flight) right? In the Phantom assistant software, go to the Basic / RC tab. see at the bottom "Control Mode Switch"? there's only 1 thing you can change, on the right the dropbox (by default) says Normal Fly. If you change that to Failsafe, then while your phantom is up in the air if you click the right switch full down the Phantom will go into Failsafe (the lights on the bottom normally green will start blinking yellow) the same as if it loses touch with the RC . wherever it is, the P will fly back to it's home position (the GPS position it locked when you turned it on) and descend until it lands. You can flip the control switch back to normal and resume control at any time (yellow blinking lights go back to green). I basically use this feature as a "fly back overhead and start descending" autopilot... especially useful if I'm WAY up in the air (at 2m/s descend rate, that's a while to descend from 200m or so) or very far off and just don't feel like manually flying back overhead. just flip the switch any time to resume normal control.
of course you'll want to test it at short range before relying on it at longer ranges... remember:
if the Phantom is below 20m and Failsafe is triggered, it will ascend to 20m, fly to home point, and descend
if the Phantom is above 20m, it will fly to home point and descend