I think I need a horn.

For my bike.  And the louder the better.  In the last couple of days, I've managed to come close to hitting two sets of pedestrians that have carefully negotiated their way past cars, but haven't bothered even casting a glance to see whether a bicycle might be anywhere in the vicinity.  If I hadn't been watching them very carefully, I think there would be some rather bruised and sore old ladies today...