Frequency: 2.4-2.4835 GHz, Bluetooth uses the globally free and unlicensed ISM band; Wavelength: approx. 12.5 cm.
There are three power classes for various Bluetooth applications, each with a different range. The most common class is the weakest (Table 1).
The effective transmission power is usually lower than the maximum power as transmission is only ever strong enough for the receiving device to pick up the signal. The receiving device can measure the transmission power and request the transmitter to increase or reduce it if possible. This power regulation prolongs battery life and avoids interference with other Bluetooth networks.
Peak transmission power (mW)
Maximum transmission power (mW)
Minimum transmission power (mW)
Table 1: Power classes for Bluetooth transmitters
This means that the transmission power, and thus radiation exposure, are not constant. Power regulation is mandatory for power class 1 and optional for classes 2 and 3.
There are various communication profiles for Bluetooth devices depending on the application. Each device only supports certain profiles. Two devices can only communicate via a common profile, and are thus only compatible if this is the case.
When Bluetooth devices with the same communication profile are in proximity, they automatically communicate with each other. Up to eight devices can be actively linked in a network known as a piconet. One device (known as the master) takes the lead and organises data transfer within the piconet; all the other devices are known as slaves.