http://www.opensc-project.org/

This is a great project,  and I believe this is a secure method of access 2 phase security need both card and key.  Also, when the key is entered wrong 4 times the card resets itself and is void.  This is mainly used for networks that need highly secure access and for financial transactions.. though I think with a little bit of work we can get something working for our door. 

http://www.opensc-project.org/opensc/wiki/PinpadReaders

This has a list of readers that work with the opensc project..

http://www.reiner-sct.com/content/view/4/16/  -- has linux drivers

we would have to construct some type of box to keep the pinpad out of the rain.  The pin pad should be connnected via ethernet.. also power over ethernet should be a option.  

http://www.smartcardsupply.com/Content/Cards/ISO7816.htm  pretty cheap, 2.80c a piece.




Though, I get the impression that we could rig this up another way, since we have some hardware hackers.. we could get a low cost smart card reader with out the pinpad.. then possibly hook up the number pad part of a pc keyboard.  This would need to goto a small node machine on the inside that would handle key comparison, software would need to be written to hand keys from the door to opensc.. I imagine though if we look close enough we would probably find a few scripts on some mailing list that would help tie things together.

https://www.scbsolutions.com/express/product_info.php?products_id=67  <- cheap smart card reader..