This is a LiPo voltage checker and warning alarm from Dynamite RC.

Features:
LED status indicator and high-pitch warning sound
Protects aircraft from unwanted landings and batteries from over-discharging
Programmable voltage threshold
Ideal for all electric vehicles, boats, and aircraft using LiPo batteries
Protects drivers from over-discharging LiPO's when using an ESC that doesn't have Low Voltage Cutoff
Monitors a battery's low voltage down to the cell level
Unit checks and displays the cell count, voltage of the overall pack and then each cell individually up to 8S
Compatible with JST-XH type balance connectors
Large digital LED display
High-pitched low voltage warning buzzer
Compatible with 1-8S LiPo/Li-Ion/LiMn/Li-Fe
Voltage detection precision to 0.01V
Low voltage alarm mode for 2-8S
When the cell voltage is below the set value, the buzzer will sound along with red LED light, default is 3.3V

Tech Specs:
Cell Voltage Display Range: 0.5V-4.5V
Pack Voltage Display Range: 0.5V-36V
Alarm Set Value Range: OFF-2.7V-3.8V
Height: 0.35 in (9mm)
Length: 1.53 in (39mm)
Width: 0.94 in (24mm)