DUO is ideal for riders who only ride with one other person or alone. Uses binary CDMA technology to communicate full duplex (conference call style) to another Duo. It is suggested for this model to be used as a rider to passenger on the same bike intercom. The Duo features Bluetooth® which allows you to pair with up to two accessory devices (cell phone, GPS , mp3/iPO D) at the same time. You and your passenger can either listen to your own music device or share one music device between the two of you.