The Difference Between a Class 1 & Class 2 Bluetooth Adapterby James T Wood
Bluetooth devices can connect with each other wirelessly through what's called a piconet -- a very small ad-hoc network. The distance that it's possible for the devices to transmit data is determined by the power of the transmitter, which is rated in one of three classes with class 1 being the most powerful and class 3 the least.
King Harold Bluetooth
When the Swedes at Ericsson invented a new wireless technology to connect devices over short distances, they wanted to call it something that symbolized the uniting of disparate things. They chose to honor the Danish king famous for bringing together the Scandinavian countries in the 10th Century, so they named the technology after Harold Bluetooth -- Blåtand in Danish. Bluetooth devices all have both a transmitter and a receiver so that the devices can communicate back and forth.
Class 1 Bluetooth devices can transmit up to 100 meters -- which works out to about 328 feet. Class 2 devices have a range of about 10 meters and class 3 devices about one meter. The way that the transmission distance is determined is by the power, measured in milliwatts, that is run through the transmitter. Class 1 devices have a maximum of 100 mW, class 2 maxes out at 2.5 mW and class 3 tops out at just 1 mW.
It Takes Two to Tango
Since the power of the transmission is related to the class of the device, in order to get class 1 transmission distances out of a two-way connection, both devices must be class 1. If one of the devices is class 2 and the other class 1, the class 2 device will limit the transmission distance to about 32 feet even though the class 1 device can transmit much farther. If you don't need two-way communication between the devices, you can get by with just having one higher-class device.
For all the benefits of the ability of class 1 devices to transmit over long distances, it comes at the cost of power. That may not be an issue for devices that can plug into an outlet to receive a constant flow of electrons, but battery-powered devices can drain the juice much more quickly when transmitting a signal across a football field instead of across the room.