@CAL.hub I use an Iris contact sensor under my metal mailbox with a small rare earth magnet on the dirk (vs the magnet that comes with the sensor). It’s been working great for at least a year now. You can see a picture in this post:
I chose this setup because my postal delivery person often stuffs large boxes in the mailbox which would knock off anything mounted in the opening. I also felt a vibration sensor would pick up wind coming down my street as I live at the end of a cul-de-sac.
