While the bulk of personal walkie-talkie traffic is in the 27 MHz and 400-500 MHz area of the UHF spectrum, there are some units that use the "Part 15" 49 MHz band (shared with cordless phones, baby monitors, and similar devices) as well as the "Part 15" 900 MHz band; in the US at least, units in these bands do not require licenses as long as they adhere to FCC Part 15 power output rules. A company called TriSquare is, as of July 2007, marketing a series of walkie-talkies in the United States based on frequency-hopping spread spectrum technology operating in this frequency range under the name eXRS (eXtreme Radio Service—despite the name, a proprietary design, not an official allocation of the US FCC). The spread-spectrum scheme used in eXRS radios allows up to 10 billion virtual "channels" and ensures private communications between two or more units.