|Silent light switch.|
The house I grew up in had switches like this one: They look like ordinary light switches, but when you flip them, there is no snap, no click, no feeling that anything has happened, and absolutely no sound. It just feels like you've moved a lever that didn't do anything. But moving that lever tilted a chamber containing a drop of mercury, tipping it onto or off of a pair of electrical contacts, and turning the light on or off. Neat for a bedroom, but so far as I know they are no longer legal due to the mercury content. At least I've never seen them in a hardware store, and these are old stock from eBay.
Source: eBay seller powerpoint-electrical-sales
Contributor: Theodore Gray
Acquired: 20 January, 2007
Text Updated: 11 February, 2007