Repeat visitors during a four-month trial will be able to check in through their phones before arrival and have their phones activated as "keys." They will then be able to skip the registration desk and unlock the door by holding the phone next to it.The short-range radio technology, known as Near Field Communication, is expected to be built into smart phones in the coming years. It is also envisioned for ticketing and card payments. Assa Abloy says it wanted to test the system before expanding it to other hotels, commercial buildings and homes.