A French company says that it has developed a way to open hotel doors using mobile phones, perhaps rendering hotel room keys unnecessary in the future.

OpenWays has designed an app for iPhone, BlackBerry, Nokia, Android or Windows-based smartphone that produces a unique audio signal that can be "heard" by a hotel room door. The firm says that guests simply need to hold their handset up to the door, press the "key" button and the door will open.

The sound is encrypted and cannot be recorded or copied, providing added security for users. Because the OpenWays' solution will be updated using the mobile data network, customers can also remotely extend their stay or change rooms without returning to the front desk.

The company says major hotels and casino chains in North America and Europe are preparing to roll out the technology, which will be demonstrated at the ITB Berlin Convention next month from March 10-14.

Last week, Aloft Hotels announced that it would pilot a check-in free service at one of its hotels, using specially-adapted RFID (radio frequency identification) loyalty cards. However, OpenWays says that its technology is designed to complement near field communication (NFC) services, which are widely used on hotel key cards but have not yet been globally integrated in mobile handsets.

"This makes the deployment of mobile key applications possible today without having to wait for 2014 when NFC phones become readily available commercially," according to the firm.