The Variations on Normal installation display by Dominic Wilcox has a very peculiar modification on the traditional headphone that is worth a look.
The Reverse Listening Device is a pair of headphones that let three people listen in on the same sound at the same time. One ear piece connects from the middle listener’s head to another’s, then the second headphone piece goes from the middle listener’s head to the other remaining person’s ear. The Reverse Listening Device gadget is just an art piece, however Dominic Wilcox states that it does indeed work, but says it sounds really weird. Though it would be difficult to use in real life, sometimes I wish something similar did exist for when you want to have multiple people listen in on something.
Wilcox’s Variations on Normal series offers a lot more bizarre takes on mundane items in a similar fashion to the Reverse Listening Device.