Mystery of The Brown Box, Solved.
For four years I have been leaving work through the same door. A few years ago I noticed a brown box mounted at the top of the door. Every once in a while I see it again and wonder what it’s for. Today I came into a work and heard “ding dong”. It turned out that brown box is the door dinger. It’s been dead for over 4 years because nobody bothered to change the battery.