RC Lipo battery low voltage buzzer alarm. This micro device can measure lipo from 7.4v to 14.8v (2s to 4s), it will sound up to 95dB if your lipo cell voltage drop to 3.3v. It is also a good device for quick test for your lipo before flight, and it can use as inflight alarm if you not sure the maximum flight time. MUST HAVE ITEM TO SAVE YOUR LIPO!!!!