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
Not phones, but TVs. My first flatscreen tv(not a smart tv yet) had a picture in picture mode, so I could play games while my family watched TV. That was nice, but it seems to have just vanished as a feature in modern TVs.
My LG C2 does have that feature, so it’s definitely still a thing in modern TVs. It feels unnecessarily hard to select what input source should go where, but maybe I’ve just not looked into it closely enough
The 3D TVs could do two different full screen pictures at the same time for this sort of usage.