Re: Occupation sensor that works with people sitting still?

["Bill Kearney" <wkearney-99@hot-mail-com>]

> A sensor placed in the doorway to the room could 'count' the number of
> occupants in the room. It would have to detect the direction of travel
> so that entering the room would add 1, exiting the room would subtract
> 1. When the count is > 0 then there is someone in the room. When the
> count is 0 then the lights can go off.

What if there's more than one exit to the room?  What if the person stood in
the door, changed their mind an went back into the room?  Entry/exit is too
imprecise and error prone to be used alone.