Bluetooth 5.0 module with hands calling. On power up, the default volume is set to the maximum. DC isolated power supply version Designed for retrofitting speakers, amplifiers, and cars to add Bluetooth functionality Helps reduce noise and electrical interference, addressing common audio quality issues NonDC isolated power supply version Suitable for batterypowered applications Intended for use with Bluetooth headsets Dual device connection Two mobile phones can be connected at the same time The two phones are paired, and the lastpaired device autoconnects on power up Use scenarios Car audio retrofit: install the DC isolated version in a car to stream music and support hands calls with existing speakers or amplifiers Home or portable audio: retrofit home stereo or powered speakers to enable Bluetooth streaming without changing the main unit Bluetooth headset or batterypowered setup: use the nonDC isolated version for portable headsets that require battery power Multidevice convenience: connect two phones simultaneously for calls and music without repairing each time Compatibility and performance notes Bluetooth version: V5.0 emphasizes reliable wireless connection and improved range Twodevice pairing capability supports convenient switching between phones Power options provide flexibility for fixed installations (DC isolated) or portable use (batterypowered)