The demonstration using the cellphone as a digital hotel room key didn’t quite go as planned. The hotel manager held his phone up to the room’s door lock and nothing happened. Realizing his Bluetooth was turned off, he tried again. Now the door’s sensor flashed green, while the phone screen informed him that the door was unlocked.

Like the majority of travelers, I had never before used a mobile hotel key, even though the first version of the system was installed nearly a decade ago. Today, about a million hotel rooms worldwide are estimated to have some version of a lock that can accept a cellphone-generated digital key, according to Nicolas Aznar, president of th e Americas division of the Swedish-based lock maker Assa Abloy . Hotels are accelerating the installation of these systems to increase revenue, drive customers to their loyalty sites, and offer a better guest experience.

The locks also accept card keys, so many hoteliers are promoting the mobile keys as an optional perk for loyalty members: When combined with online check-in, guests in countries that don’t require a passport to be shown can go directly to their rooms without a stop at the front desk. And, since the keys are downloaded electronically through a hotel app, the host has a presence on the guests’ phones, and can offer other exclusive services, like promotions and a chat feature.

“Had my first hotel stay where human interaction was utterly unnecessary. Online booking, mobile check-in, mobile room key, and mobile check-out. I was a single smile and wave from not seeing a single hotel staff member my entire trip,” Victor Wieczorek wrote on Twitter under the handle @vwieczorek.