Nicole Prause is a sex researcher who wanted to design a gender-neutral orgasm-measuring tool that would fit in the anus and detect and measure pelvic contractions but all the buttplugs she tried to modify ("We ordered like 20 of these butt plugs off Amazon, and it messed up my recommendation engine for all time") were designed to be pistoned in and out, and thus had a taper that made it prone to popping out at the moment of orgasm.
Prause tweeted about her troubles and forged a partnership with a German cosplayer who had extensive 3D printing experience; they designed a research-optimized butt-plug they call the "anal pneumatic base for psychophysiology research" and released it as an open source hardware design that you can download from Thingiverse and 3D print at home or work.
Prause can explore a range of questions beyond the physiology of the orgasm. This includes direct health problems like postorgasmic illness syndrome, in which men are struck with headaches and fatigue following ejaculation. It might be due to some sort of autoimmune response to ejaculate, or it might have something to do with the number of contractions these men have, which the device can measure.
"We want to make sure there are no distinct qualitative differences between the climaxes of those patients and the control population," says Prause. "We don't currently have a reason to believe that would be the case, but if there is then that leads us down a very different path."
The Strange Saga of the Butt Plug Turned Research Device [Matt Simon/Wired]