I just don't see how, if it's a 'trusted area' you don't usually lock your screen (or maybe you do? I imagine most people don't though), which means if you're logging back in, it's because you've been away for a bit.

In which case, your machine may also be hibernating, which is slow to being with. So something like automatically unlocking while your phone is around isn't really all that useful.

Not to mention, how long does it take to type in a password?