For me its the ‘Knock Code’ that LG had on their phones (I really wish LG still made at least the V series phones)
Basically there was a four-square area and you set up a sequence of where you would tap to unlock the phone. That set of squares was only shown when you set up the code
Then, to unlock your phone, you would tap those areas in the sequence you set up (even with the screen off).
Fingerprint readers are nice, but I really do miss the knock code
Edit: did find this article with a way to do the knock code, but if done wrong, could brick your phone I guess.
Plus, article is from 2014. When I looked at XDA’s info on it (they also being the developers) it looks like development on it is over, but individual modules may or may not still be supported by their devs
You can also slide up from the bottom of the screen to get to the task switcher UI, and there’s a button allowing you to select text (even from an image with text in it) and then get a translation of it. IMO, this is even better than it used to be for getting translations because it works with nearly everything except certain financial apps.
Edit: oops, that message didn’t format very well, fixed it!