This is a GPRS / GSM Arduino expansion board developed by Keyes. It is a shield module with frequency of EGSM 900MHz / DCS 1800MHz and GSM850 MHz / PCS 1900MHz, integrated with GPRS, DTMF and other functions. It supports DTMF, when the DTMF function is enabled, you can get the character feedback from the conversion of button pressed down during the call, which can be used for remote control.
It is controlled by the AT command, you can directly start its function through the computer serial port and Arduino motherboard. The SIM800C GPRS Shield board has a built-in SIM800H chip with good stability.