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
Maybe a better term is field-replaceable batteries. It’s great for the longevity of a device to be able to install a new battery in a few minutes with just a screwdriver, but I miss the earlier days of cell phones where you could keep a spare battery in your bag while out and about and swap it out with the dead battery in your phone in just a couple seconds.
Well, in my opinion battery banks works better for this (and they weren’t available in early days). And they are much easier to recharge :P
EDIT: and works with every device