Bluetooth is a personal area networking (PAN) technology using the 2.4 GHz frequency band for short range communications. Originally developed to replace the wired headset for cellular telephones, Bluetooth technology has expanded to work with multiple devices including speakers, printers, handsets, stereo headsets, and is emerging in the eHealth / telehealth device arena. Bluetooth uses the IEEE 802.15.4 physical layer with a Bluetooth communications protocol stack.