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BLUETOOTH
Security is taken care of through the frequency hopping and 40-bit encryption. As the system uses radio, it сan work through some barriers – briefcases, shirt pockets and desktops, for example – but it won’t carry through office buildings. The power level of the transmitter can be varied, with feedback from the remote side of the link used to set the output to the lowest level commensurate with error-free operation. This saves power and increases the usable density of devices.