So if I'm going to start a new thread, you had better bet that it will be on a random piece of trivia / curiosity. But I've noticed something in the past months and wonder if others encounter it. When I check out of a room using the mobile application, I'll sometimes get a single, solitary ring of the in-room phone about 30 seconds later. No one there if I pick up the receiver, and only one ring. More curiously, I've only encountered it at Doubletrees, not at any other brand. Personally, I like it as a confirmation that I'm checked out, and frankly it's pretty impressive if the systems are in fact integrated that well. But I'm also curious if this is chainwide, systemwide, or random. So, do others run into this, and if so, at what properties?