We had a CAC reader on the back door of the finance office. Saw a private trying to figure out how to open it, and heard someone on the other side of the door. I told him it was DNA activated and if he beathed on it, it would open if he was supposed to be there. He leaned down, blew on it...and the door opened. Took him three weeks to figure out what it really was, and the reason sometimes it didin't work was "because he wasn't blowing hard enough."