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
Notifications that don’t take up a big chunk of your screen.
I remember when notifications were just little icons at the top of the screen that represented the app, not three or four lines of text, or a picture, that let everyone nearby know what it’s about.
I’ve had times in the past where I’ve been playing with my kid on the phone, or reading a book or something, and a friend will message me something inappropriate. It opens on the top of my screen before I can do anything about it, and for no reason. I have to open the app anyway to see the full message.