Bluetooth devices communicate using radio waves, your Bluetooth phone and headset do not need to be in a line of sight. The two devices only need to be within a maximum of 10 metres of each other, although the connection can be subject to interference from obstructions, such as walls, or from other electronic devices. The headset is specially designed for Nokia phones that support Bluetooth wireless technology. The headset can, however, be used with any compatible Bluetooth device that supports the Handsfree or Headset profile. ("Profile" meaning a set of Bluetooth commands that your phone uses for controlling the headset.) The headset provides the best prerformance when it is used with a compatible Nokia phone. If you use the headset with a phone produced by another manufacturer, all the functions described in the user's guide may not be available.