Yikes!  I have only heard about one ES and one Columbia that had a door open and what I heard was that there was "some damage" to the stabilizer.  Sounds worse than that!  As best I know, the two aircraft that lost their door both had the "early" design with two pins that hold the door shut.  The later ES's like mine have the IV-style over-center latches.  There has been an argument made that these can't come open in flight, as the outward force on the door holds the hook engaged.  I don't know if that is true, but I've not heard of a IV door that opened in flight.  Regardless, I have a switch that detects and over-center condition of the latch.  And one that verifies the baggage door is locked closed.  that said, I like the audio alarm that has been proposed.  I know the "ANGLE ANGLE PUSH" gets my attention every time.

Gary Casey