They will get notified that their room is ready and then breeze past the front desk while checking in and getting their room and credentials via the mobile app. Once at the room, they can wave their phone in front of the lock and it should open. The app will open doors for 170,000 rooms at 250 U.S. properties within the Hilton Hotels & Resorts, Waldorf Astoria Hotels & Resorts, Conrad Hotels & Resorts and Canopy by Hilton brands.

Already guests have digitally checked in more than 5 million times so far, and the digital key testing has started this month at the Hilton Alexandria Old Town in Alexandria, Va. For now, beta users need an iPhone but it will be available to Android users later this year.

The smartphone-based keys use Bluetooth technology inside the handsets to unlock the doors, and require the user to open the app and put their phone next to the panel of the door. If the user doesn’t have the app or the phone, she can get a traditional key card from the front desk, which might come in handy if her phone is out of juice. Hotels like the smartphone “keys” because they increase guest satisfaction and the likelihood of a customer booking a room through the hotel’s apps or site instead of through an online travel site such as Expedia.

Aside from the new smartphone “keys” the digital check-in also helps hotels manage their inventory because customers can tell the hotel when they are arriving, which then helps the managers schedule cleanings and figure out where to place guests. By enticing users to use the mobile app for booking, hotels get more revenue, but ensuring that they continue using the app throughout their check-in and stay the hotel is also gathering data about the guest that helps the hotel understand usage and traffic patterns that can dictate cleaning, build guest preferences and eventually the best time to stock the mini bar. That means a better experience for the guest and more business opportunities for the hotels.