Gee, that wasn't too weird at all

This morning when I woke up, I found it to be incredibly warm in our bedroom. After kicking off all the blankets and moving as far away from any warm bodies as possible, I silently begged the furnace to stop pumping hot air into our bedroom. I watched the clock for ten minutes, the whole while the furnace churning away. At this point, I seriously started to consider the possibility that the furnace was broken and would never turn off again.

I went downstairs to check what temperature it was set to and was very surprised to see that our front door was wide open. It had obviously been this way for quite some time judging by the frostiness of the air downstairs and the non-stop action of the little furnace that could.

I closed and locked the door then went up to the bathroom where Liam was having a shower to ask him why the door was open. He had no idea either. The last time either of us had paid attention to the door was when he locked it before he went to bed and I checked it a few minutes later on my way to bed.

Weird.

In the half hour or so since this incident I have come up with the following possibilities as to how our front door became unlocked and opened while everyone was still in bed:

1) Liam was sleep-walking and opened it himself.
2) Fingers was really bored and spent all night working on it.
3) Lillian knows a lot more than she's telling us.
4) Someone broke into our house without leaving any footprints in the snow then decided not to steal anything.
5) The Leddys somehow ended up with a working key to our house and thought it would be funny.
6) Some not-so-funny ghost has taken up residence in our house and wanted some fresh air.

Seriously, people, somehow our door ended up open and none of us has a clue. I'm open to suggestions here. As for now, I've got both the handle and the deadbolt locked and I'll be more than happy when the sun comes up this morning. Creepy.