Earlier quoted context omitted.
Signal Desktop works without having your phone turned on. It acts like a full, independent client after linking it to your smartphone app (unlike WhatsApp, which does require your phone to be turned on).
wow, sorry. my bad. So I guess there is a way to use signal without having a phone nowadays! That's a great news! I will try right now.
Edit: It actually has the option to register without smartphone, but it's only enabled in the debug versions.