If none of the two connected devices are on a call, the call audio comes from the device that first receives an incoming call. If device A has a call in progress, and you receive an incoming call on device B, Ear (open) plays the ringtone at the same time. If device A hangs up, Ear (open) switches the call audio to device B.
If you have any further questions about Dual Connection, please check the description on nothing.tech, or contact our Customer Service.