> well, some practical tests will be necessary

You would be able to tell quite quickly whether your method will
work by doing something like opening the fridge or freezer door and
seeing if the cold air flowing out can be detected against the warmer
kitchen. I think though PIR sensors are too slow to react at walking
pace and the signal will be quite "wobbly"
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist