I tested the idea with a reader I bought used. It was not easy to get working under Linux, But I did finally make a cool unlocking system for my laptop. At that point there was nothing to do but try breaking in. I'll be damned if I did not get in about 10min later. The solution? I dusted a fingerprint with graphite dust, then lifted it with tape and attached it to paper on my finger. That's it.  Way to easy to defeat.