Bluetooth uses the license-free frequency range from 2.402 to 2.480 GHz for wireless communication. This frequency range is also referred to as the ISM band. It has been designated for license-free use worldwide, but is subject to interference from other technologies. WiFi networks, cordless phones or microwave ovens can influence the Bluetooth signal quality.
Bluetooth is divided into three classes, according to the maximum transmission power. Class one reaches ranges of up to 100 metres, at a maximum output power of 100 milliwatts, but at the other end of the scale, the typical operating range of class three Bluetooth is one metre, with a transmission strength of one milliwatt.
The Bluetooth standard has been revised several times since the release of version 1.0 in July 1999. Most recently, versions 4.0, 4.1 and 4.2 have been published, which are supported by newer devices. The main focus of development in recent versions was the implementation of security mechanisms, higher transfer rates and lower power consumption through special power-saving modes.
In telephony, the Bluetooth standard is often used for the wireless transmission of voice data between headsets or hands-free car kits. These hands-free kits enable Bluetooth connections to mobile phones, so that the driver can make or receive calls without having to hold the phone in their hands. In addition to the transmission of voice data, the standard can also be used to establish telephone calls or to send data from address books to the in-car hands-free system.
In addition to use in cars, many people use a standard Bluetooth headset for wireless communication with their phones, giving them the maximum freedom of movement. By pressing special buttons on the headset the user can answer telephone calls.