Why a Mercury Switch?

Here's a story to start with:

When my brother was a teenager and I was still little, he drove my parents nuts by tipping his chair back at the supper table. None of the standard parenting approaches could stop him - not nagging, threats, or bribes. An engineering solution was called for.

One day when my brother was out, my dad assembled and affixed to the underside of my brother's chair a buzzer activated by a mercury switch. That is to say, when the chair tipped back, the mercury would flow to the business-end of the device, make the electrical connection between the wires, and the buzzer would sound.

We all sat down to dinner that night, and presently my brother tipped back in his chair. Bzzzzt! He set his chair down and looked at my mother, who was well-known for leaving entree-level food in the oven that would buzz its readiness for consumption during dessert. No reaction.

Apparently deciding he must have been hearing things, he went back to eating and soon tipped back again, activating the buzzer. This time he set the chair down, then very deliberately and slowly tipped back once more, and finally looked under his chair. Our suppressed laughter exploded then and this particular legend was born. Did it stop him from tipping back? I don't remember, and probably not, but that was no longer the point.

So what is the point? If you're an ACoE you probably already know. Maybe you are the spouse of an engineer, in which case you get bonus honors. Tip the switch, share your stories and memories, and let's see if there are as many connections as I have always thought.