In my never ending search for the simplest method of doing things, I have come across what is known as a latching reed switch. In an article referenced on this forum. By whom I can’t remember just now, the writer talks of reed switches and how to modify them.
In one paragraph he has used a normally open reed switch and two magnets to create a latching reed switch.
I can’t say that I fully understand his theory. Here is an excerpt from his article;
"The idea is to glue a small magnet and the reed switch to a base so that the magnet keeps the switch’s contacts closed. When another magnet comes close it interacts with the first magnet’s field enough to open the contacts back up giving us a NC reed switch!
First glue the reed switch to a piece of Plexiglas or other non-metallic base material. I found that the reed switches that I used worked best if the reeds inside of the glass vial were held in a vertical position. Next attach an LED or other light and battery to the reed switch so that you can tell when its contacts are closed. Put the small magnet on the bottom of the Plexiglas and move it around until the reed switch’s contacts close and the light goes on. Now bring another magnet near the reed switch and see if the contacts open again. It will probably take a bit of experimentation, and at least 3 hands, but you should be able to find a position for the first magnet so that the reed switch reliably keeps its contacts closed but opens them when a second magnet is nearby. Once you find a location that works well glue the magnet in place. Below are three NC reed switches that I put together while testing. Each of them has a small reed switch on one side of the Plexiglas and a small magnet strategically placed and glued on the other side."
If he is using a normally open reed switch with a magnet placed so that the contacts are normally closed. Then passes a second magnet over the assembly, wouldn’t the contacts open for only an instant? I fail to see how this is a latching reed switch.