The best invention anyone could come up with would be an unbeatable lie detector. It would put defense attorneys pretty much out of business - a lawyer’s job would be to keep his client away from the lie detector at all costs because once hooked up the truth will be revealed. It would put 99% of today’s politicians out of business as well.
H. Beam Piper’s “Little Fuzzy” includes an unbeatable lie detector used in the courtroom - not sure I’ve seen it used anywhere else. Doc Smith’s Lens served the purpose as well now that I think about it.
The lensman series is excellent. Unfortunately, it wasn't really written for a universe inhabited by human beings. Even men of pure motives can be led astray.