Just found (via Chad Everett) a Japanese website with images showing an automatic door that has horizontal strips that detect how far to open to let you in. As far as keeping the cold/heat out etc. they could be onto something. Even better if you paint the outsides of the strips to resemble a wall or some such feature - you have a secret door!
http://www.e-taf.co.jp/cgi-bin/e-taf/sitemaker.cgi?mode=page&page=page2&category=0