This is the wireless battery voltage checker/alarm, it contains two modules TX and RX, the TX is mounted on board (on the rc aircraft), and when the monitored battery voltage is low, then the RX (mounted around you on ground) will alarm go off.
It enables you to monitor the on-board battery voltage.

Specifications:  
Operating Voltage: 4-9.6V
Alarm Voltage range：3.3V-50.4V（LIPO 1S-12S）
Weight: 2g
Wire Length: 17.2mm 

Package includes:
1 No: RX module
1 No: TX module


Download Manual HERE