There’s one wearable technology that, for sheer amount of time on screen and number of uses, eclipses all others, so let’s start with that. Star Trek: The Next Generation introduced a technology called a combadge. This communication device is a badge designed with the Starfleet insignia, roughly 10cm wide and tall, that affixes to the left breast of Starfleet uniforms. It grants its wearer a voice communication channel to other personnel as well as the ship’s computer. (And as Memory Alpha details, the device can also do so much more.)
Chapter 10 of Make It So: Interaction Design Lessons from Science Fiction covers the combadge as a communication device. But in this writeup we’ll consider it as a wearable technology.