When I use a GUI updater, sometimes it says that my computer needs to be restarted.
But when I use
apt-get upgrade for example, I can't find messages like this.
I saw this answer, so do I need to check manually which packages were updated?
See this ServerFault answer: after updating with
apt-get, you can check for the presence of
/var/run/reboot-required. You didn't mention what operating system distribution you're using, so you may want to double check that your distribution does indeed behave this way.