Last month, I wrote about how Hilton is starting to give guests the ability to check-in via mobile device. Yesterday, Marriott announced that they will be expanding their own mobile check-in/out program from their initial 500 Marriott branded properties to over 4,000 worldwide Ritz-Carlton, JW Marriott Hotels & Resorts, Renaissance Hotels, Autograph Collection, AC Hotels, Courtyard, SpringHill Suites, Fairfield Inn & Suites, Residence Inn, TownePlace Suites and Marriott Executive Apartments.

Here’s a short video clip from Marriott on how mobile check-in works.

Marriott Rewards members get a notification on their mobile devices at 4pm the day before arrival, and then an automatic alert when their room is ready. Once difference between Marriott and Hilton’s mobile check-in process is that Hilton plans to allow guests to bypass the front desk starting in 2015 by using their smart phones to unlock doors. After checking in via the app with Marriott, you will still need to stop by a mobile check-in desk to pick up your key card (and show ID, which I think is a good thing).

Marriott also introduced mobile device LocalPerks, which are push notifications for offers while at the property. I haven’t used this yet, but I’m hoping it would have things like an extra percentage off when dining in the restaurant or a flash discount for spa treatments.

Marriott says half a million people have used mobile check-in so far, and 9 out of 10 guests say they would use it again. Have you used it? If so, how did you like it?