The Limited range models are ideal for riders who only ride with one other person or alone. The DUO Pro model 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/iPOD) 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. When riding alone you can still be in touch by having your cell phone and/or music device paired. This model is deal for the rider who commutes on a daily basis. Available in either full or open face depending on your helmet style. The DUO kit includes the following: Unit, noise suppression Hi-Fidelity headset, factory installed Lithium Ion rechargeable battery, mounting hardware, wall charger and users manual.