My partner Sohyun and I have thought about our micro bit project.  We figure it would be smart to have a little alert/reminder for when you forget to lock your door.  We also think we could add a reminder that surfaces on your phone.  It could be a light that goes on as well, so when you see it you would know to lock your door.  This was our first good idea that could be very helpful to some people, but it still needs some revisions.