Home Alarm System 1,Touch keypad,Big LCD display 2,GSM+PSTN dual ... with Contact ID protocol(alarm information, status information, AC power off and recover, Low voltage, test) 8. Support wireless “ding-dong ... *1AC/DC Adaptor*1User manual*1 FAQ of GSM Security System:1: About GSM frequency: it can support 850/900/1800 ... connect with us freely......... GSM+PSTN Dual-network Home Alarm System