I think we'll have to get one of those in/out boards that you sometimes see in reception areas.
I have just mentioned that my ds is late getting back from his outing only to be told that he's been back 2hours and is upstairs.
Apparently I was in the kitchen when he popped his head around in the other room to say he was back.
The older ones come and go and I'm not sure anymore who is in and who is out and when.