Lauren McCarthy's "Happiness Hat" forces you to smile and, if it detects that you're not smiling, provides "pain feedback" in the form of a pin in the back of your head.

The Happiness Hat is a wearable device that detects if you're smiling and provides pain feedback if you're not. An enclosed bend sensor attaches to the cheek and measures smile size, a servo motor moves a metal spike into the head inversely proportional to the degree of smile. Through repeated use of this conditioning device you can train your brain to smile all the time. This is the first in a series of Tools for Improved Social Interacting.

happiness hat from Lauren McCarthy on Vimeo.