1-8 Cell LiPo Battery Voltage Checker with Programmable Low Voltage Alarm from GT Power
Features:

Checks the voltage of each individual cell (up to 8 cells) and also displays the total voltage for all cells
Built-in audible low voltage alarm can be set to warn of low voltage conditions before flight. Alarm is pre-set for 3.3V but can be set to any value between 2.7V and 3.8V
Automatically protects against reverse connections
Helps protect your battery from overcharging or overdischarging

Includes:

LiPo Voltage checker

Specifications:

1-8S Lipo\/Li-ion\/LiMn\/Li-Fe
Voltage detection precision: 0.01V

Unit voltage display range: 0.5-4.5V

Total voltage display range: 0.5-36V

1S test mode voltage range: 3.7-30V

Low voltage alarm mode for 2-8S

Alarm set value range: OFF and 2.7-3.8V

Dimension: 40 x 25 x 11mm

Weight: 9g