Back in the stone age before the internet, iphones, wifi, bluetooth, etc. I designed and installed a remote level indicator and refer temp alarm for my trailer that had a read out in my Van. It was done by brute force with 12 glass mercury tilt switches and at first a box and then a round dial with 12 pilot lights. The mercury switches were mounted on a board using the glass fuze holders and calibrated to come on when one side or the other of the trailer was 1,2,4,6,8,10 inches high. All this was connected by a bundle of telephone wiring with like 20 to 25 wires and included a refer alarm that consisted of a set of contacts separated by an actual sliver of ice kept in the freezer where if it thawed the contacts would send a signal that activated a light and a buzzer in my Van co located with my leveling system indicator lights. It all worked great from 1982 to 2007 when I got my current trailer and went with the GIANT levelmaster bubble level that I can easily read from my Van. The refer temp/thaw alarm by then was replaced with remote reading thermometers which weren't a common consumer item back in the early 1980's. Sorry, no pics.
Larry
