I woke up tonight at 4am in wonderland with "ALISSE" in my mind.
Well, ALISSE is what I call an Automatic Liftbag Safety System that could be used while training freediving.
ALISSE is made of a couple of liftbags and bottles of compressed air with a configurable timer countdown.
We could set ALISSE timer to automatically inflate the liftbags after a predefined amount of time. (like Freediver Recovery Vest developed by Terry Maas).
After setting the timer on surface, we drop ALISSE along the rope until it reaches the bottom plate/weight.
Then we do our dive with the usual bodyline attached to the rope and after the predefined time elapsed ALISSE will come up and could bring us to surface in a case of need.
At surface, we just need to empty the liftbags and reset the timer for a new dive.
You can follow the discussion at DeeperBlue.