niceeshop(TM) 7.4v 11.1v Low Voltage Buzzer Alarm Lipo Battery Voltage Indicator Tester Checker (Red) Material:plastic+metal The alarm sound and red lights to warn you when the battery voltage is too low Will buzz and turn on red LED light when voltage is less than 3.3V Useful in flight when you cannot see the lights Good for 2 Cells (7.4V) and 3 Cells (11.1V) Li-Po Batteries