Bluetooth is a standard for the wireless Transmission of small amounts of data over short distances. It is designed particularly for mobile devices (mobile phones, headsets, etc.) because the transmission does not consume much energy. It can reach speeds between 1 mbps (version 1.2) and 3 mbps (version 2.0 + EDR ).
Transmit power and so the range is devided into classes: Class 1 is capable to cover 100m under ideal circumstances, class 2 is about 10m und class 3 ca. 1m. Most of the mobile phones are class 2 devices and cover a 10m range. Dongles for the USB port are mostly class 1 devices. The covered range is limited by the "smaller" comminutaction partner. So it does not make sense to buy a class 1 dongle to exchange data with a class 2 mobile phone. The range will be limited to 10m.
The bluetooth standard contains diverse profiles, that are based on the simple data exchange and define (ideally manufacturer independent) protocols for various applications. Examples are
- DUN: connect a PC over the phone to the internet
- FTP: File exchange
- A2DP: Music transmission to headphones
To secure the data transmission, the to devices participating in the communication have to be coupled the first time they are connected. To do that it is required to enter the same pin on both devices. Some devices like Headsets have a hardcoded pin. When coupling two devices, they create an encryption key that is used in the following data transfers, so that it is not easily possible to eavesdrop the transmitted data.