In-Line Battery Voltage Alarm with LED XT60 Plug For 2-6s Lipo Battery
Description (From Banggood):
This super cool voltage monitor sits in line between your esc and battery. Simply select your desired per-cell voltage cutoff by holding down the button until it starts flashing. Once you have your voltage selected, leave leave it on the selection until it stops flashing. When flying, the loud buzzer will activate as well as the 5050 sized LED to alert you to land. Perfect for short range FPV or line of sight flights!