Voice active monitoring .
Built in adjustable sensitivity voice active microphone.
Built in High sensitivity monitoring amplifier microphone  
Easy to operate - Open the back cover can insert the Sim card
Built in rechargeable polymer LIION battery, with capacity up to 4200mA
USB charging ways, can be used while charging.
Built in charger circuit allowed using in charge mode.

specification:

GSM band module:  900/1800/1900
Voice sensitive:  -75db  
Standby power consumption:  6mAh
Working power consumption: 200mAh  
Power:  3.7V  4200mA
Charger power:  5VDC at 500mA
size:  110x60x40mm