At university, we once built a networked doorbell system for the offices. Lots of small displays with a button outside the doors, connected on a CAN bus to a co

At university, we once built a networked doorbell system for the offices. Lots of small displays with a button outside the doors, connected on a CAN bus to a controller, that you could configure, and another device in the office to make noise and control the screen. We had a problem, though: The door display devices would randomly crash and require somebody to go over and reboot them. This was very annoying, and we could never reproduce it. We added monitoring for it, and after a while the problem mostly went away on its own. But half a year later, it was back. It seems the system worked fine in summer, but started crashing in winter. We finally, after much testing and deliberation, realised it was caused by the devices having a metal front plate which would easily attract static shocks, which would crash the device. And in winter, the dry air and wooly clothing would cause a lot more static discharges.