ORIGINAL: Silent-AV8R
The Futaba radios that offer low voltage failsafe will typically just move the throttle to a low position. You can reset for about a minute by moving the stick to low and then back to high. The 12 and 14 channel radios allow you to set a battery failsafe (B-F/S) for all channels. Otherwise the other channels simply hold their last good position.
This feature operates at about 3.8 volts. The Futaba FASST receivers have been shown to continue to operate down below 3 volts. Some digital servos (non-Futaba) will stop working at 3 volts.
I have suggested several times to Futaba that they make this feature adjustable by the user so that you can set the voltage to a more useful one for your battery system. I mostly fly using 2S LiFePO4 packs and if I get to 3.8 volts my packs are essentially dead. I have never had this feature actually operate for real while flying, but it is there.
The second sentence of the first paragraph may a little misleading. The 12/14 channel radios do allow for (B-F/S) for each channel or a hold, as stated but also you can select a predetermined value that you can set. It would be slick if you got an audio alarm instead of the throttle being retarded to let you know of the low voltage. Perhaps a sultry female voice saying "(fill in the blanks __________________)
Howard