This simple to use LiPo low voltage alarm is small and light for on board use. It plugs into balance lead for detecting low voltage on individual cells.
A loud alarm will sound and LED will change from Green to Red if any individual cell drops to 3.3v or below.
This little device is great insurance to make sure that not only do you not discharge your LiPo pack too far, but you won't loose a model due to a flat battery.