Starting in June, the Intercontinental Hotel Group is testing out the use of smartphones as room keys. Travellers stayed staying at the Holiday Inn Chicago O' Hare Rosemont or the Holiday Inn Express Houston Downtown Convention Center can download a distinct audio code into their iPhones, Blackberrys or Androids. Passing the phone by the door lock will open it and they will bypass the front desk altogether.

Another hotel chain, Starwood, is one of many experimenting with radio frequency identification, or RFID. At their Lexington, Massachusetts property, the Aloft Hotel, they are equipping guests with RFID cards. The RFID card is programmed to open that door automatically. As commented by the hotel chain representative, RFID keying systems are more common than audio-based ones.

Source: Readwriteweb, Hotels test smartphones as room keys (28 May 2010)