Hi Wouter, I think an IR- type is prefereable (not a "chemical" CO2 sen= sor). I have found this (but don't know the price...) http://www.gene= q.com/catalog/en/air_quality_monitor_yes-206.htm good luck.. MarcoG=0D = ---------- Initial Header ----------- From : "pic microco= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body