CARSCOP add the internal or external microphone for CCTR-804 4G GPS tracker by client request, form July 1, 2019 client can select internal or external microphone version of CCTR-804, the listen function can be controlled by SMS command and finished by phone calling, so the SIM card need enable SMS & voice function & Internet data visiting (M2M iot sim card may not be used for listen), the new version board use global frequency band 2G/3G/4G module, can cover most of the mobile phone network frequency, so it can have  better network signal, for detail please contact us.