Answer: Gambling

While electronics miniaturization has made all manner of devices small enough to wear, in the early days of computing, it was quite a feat to shrink a computer—however primitive or task-specific—down into a wearable package.

The first wearable computing device comes to us courtesy of Edward O. Thorp and Claude Shannon—better known as the fathers of card-counting theory and information theory, respectively. In 1961, the two of them sat down and built a cigarette pack-sized analog computer designed to predict the outcome of roulette games.

The wearer controlled the device via micro-switches within their shoe and the device would report back to the user via musical tones broadcast to an in-ear radio receiver. Although successfully tested, hardware problems prevented the device from seeing regular use at the tables. Over the next two decades, technological improvements would lead to a variety of enterprising individuals creating shoe-based computers in an effort to out-maneuver casinos.