Bluetooth may be the oldest short-range wireless technology. It debuted in 1998 as a cable replacement technology. The IEEE originally standardized it as 802.15.1 but no longer handles it. Instead, the Bluetooth Special Interest Group (SIG) maintains and develops it. The SIG also certifies Bluetooth devices for interoperability.
The basis of the standard is a radio that works in the 2.4-GHz industrial, scientific, and medical (ISM) band using frequency-hopping spread spectrum (FHSS). The modulation is Gaussian frequency shift keying (GFSK). The original standard featured a gross data rate of 1 Mbit/s, but that has been upgraded several times. Later versions upped that data rate to 3.1 Mbits/s using several variations of phase shift keying (PSK). The maximum range is typically less than 10 meters, although higher-power versions can reach farther.
Bluetooth may be the most widely deployed of all the short-range wireless technologies. The fact that it is in most cell phones today for wireless headsets means that billions of Bluetooth radios are deployed. It is also very widely used in vehicle hands-free systems and wireless speakers. As of the end of 2012, there were more than 9 billion Bluetooth chips out there in various devices. More than 2.5 billion chips were shipped in 2012 alone.