Electrodes. Tiny electrical-impulse relays that are sometimes sticky, oftentimes not, that press against one's body in an indefinite number of locations, hooked up by thin wires to a USB 5.0 relayer (USB 6+ specifically disallows trodes). Trodes are meant to be tactile reponse devices, which is to say when you reach out to touch an object on your screen, you will "feel" the object because the trode buzzes your body in the appropriate places. It's possible to trick the body into letting you grip something tightly, or brush it lightly. It was the next "big thing" in computers in the 2020s, until the inevitable happened...
Trodes are used on many interesting parts of the body nowadays. A lot of time the head. And with an amplifier hooked up, it creates a fantastic buzz unlike anything you've ever felt. It's not that the effects are as intense as what you'd get from chemical interactions in the brain, but the charm is that you can't program or fine-tune something you inject. The first killer app for trodes was to hook them up to the visualizer in iTunes, and bask in the crazy graphics, both onscreen and off.
There were studies done a few years ago that linked trode use (even mild trode use) to brain damage, epilepsy and ADD. No one knew for sure how reliable the studies were (they were funded by conservative parents' groups), but the effect put a chill on the industry. Only a few manufacturers in Malaysia still make trodes at all, and even the typically stubborn Illiayson Technologies dropped support for trodes in Transfire 5.