Features: 1) Industrial GSM module 2) Voice volume adjustable 3) Reverse-battery signal provided 4) Network management through SMS 5) Standby battery available 6) Preset local handset numbers and block numbers 7) Locks of network, SIM card, and the and card 8) Preset local prefix and IP access number 9) GPRS wireless online 10) Connected with telephone and charging system Specifications: 1) Frequency: GSM900/1,800/1,900MHz 2) Power supply: 110~240V AC, 9V DC 50/60Hz 3) Working temperature: -10 ~ +50°C 4) Working humidity: 10%~95% 5) Air pressure: 86~106KPa