Other Macs
Sign in with the same account on another Mac you work on, the same way as before. Please don’t share your account with other people. Macs you use as displays need no account at all.
Offline
Second Display checks your licence whenever it’s online and keeps working offline for up to 30 days after the last check. In the last days it reminds you quietly in the menu, for example “Licence check needed within 3 days. Connect to the internet.” After 30 days offline it needs one check before it connects a display again.
A trial works offline until it ends.