Good article on hall effect switches and latches that can be soldered on pcb boards and used to detect the presence of a magnetic field and converting that to a digital signal.
I like the latching. Was one of the issues we had with the elevator and the hall effect sensors. We had to wait a certain amount of time so that it would not recognize the same magnet more than once. The latching would have make it work exactly how we wanted it to. We might want to see if we can get a catalog or something for sourcing some of these electronics.