I love the idea, but I don't think I could trust myself with it. Generally my phone will still have a healthy chunk of battery left at the end of the day, but fairly often, if I'm out of town for a day for meetings or whatever, by the time I'm back home I will have spent so much time on calls that it will have completely drained my battery.

One feature I'd love to see is connecting it with the doorbell, then I would forget about my battery worries and go straight for it. Would come in occasional use for if someone you're happy to let in arrives while you are out, but would also be great for day-to-day use. They press the buzzer, you get a phone call to talk to them followed by the option to let them in or not. (Where I live right now, my office is two floors up, it's pretty rare that I can hear anyone at the door.)

edit: The FAQ page is a bit vague about international orders due to "latency issues", any chance of some expansion on that? To my mind, a long distance (say, UK to California) is adding less than a second of latency, and I wouldn't have any problem if the door took a couple of seconds to unlock. But maybe I'm misunderstanding the problem latency causes?