my current oldest is a psion organiser from 1997. 2mb of offline storage. a full qwerty keyboard, word processor, spreadsheets and database in a tiny portable case running off 2 aa batteries. great for storing passwords in an unhackable format :-)
i describe it as 'unhackable' as it has no connection to the internet. if stolen the password on it will deter most if not all. these days it's simply a matter of time before any device connected to the internet is hacked sadly.
I would consider it as unhackable simply as vintage tech that might befuddle a certain class of adversaries in much the same way a stick shift stymies car thieves or rotary phones confuse my younger neices and nephews as to its operation.
https://en.wikipedia.org/wiki/Psion_Series_5
i prefer the keyboard over the series 5. it can run for over a year on 2 aa lithium batteries at low usage. about an hour per month.
i keep meaning to sort out a rasp pi sidecar so i can use the psion as a terminal to a full linux system for mobile computing but haven't found the time to do so. https://www.tomshardware.com/news/raspberry-pi-psion-sidecar
i describe it as 'unhackable' as it has no connection to the internet. if stolen the password on it will deter most if not all. these days it's simply a matter of time before any device connected to the internet is hacked sadly.