Mobile phone owners can now use their devices as room keys at some Starwood hotels. A tap of the phone on the door lock and it will let you in, no more losing of key cards or locking them in your room then.

As the eager eyed among you may have spotted from the picture that's an older iPhone without NFC, so how is it unlocking the door? Bluetooth. Starwood hotels, who owns the W, decided to use Bluetooth rather than NFC making it accessible to all phone owners.

At the moment Starwood is rolling out the locks in 10 of its hotels but plans to install even more, at 140 locations in total, next year. If you're old enough to remember room keys being replaced with keycards you'll know changes catch on fast. So expect to see mobile operated locks as commonplace soon.

What happens when your battery runs out though? This hasn't been made clear but presumably, as you'd do when you lock a key in your room, you'll be able to head down to reception to get a card or charger for you phone.

At the moment the locks require you to open the app and turn on Bluetooth before tapping. While the app is great for telling you the room you're in and allowing you to check-in without queuing at the desk, we'd find the process a little long compared to a key tap. But it's something to do in the lift up perhaps.

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