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
Or even just the navigation buttons being separate from the screen.
I really miss how the blackberry volume rocker buttons would seek media on a long press
My oneplus does that when the screen is off. But you just reminded me how much I miss my blackberry curve, that thing was rad. One gripe was the trackball would get filthy, then they released the touch track thing.