Without a license key, Little Snitch runs in demo mode, which provides the same protection and functionality as the full version. The demo runs for three hours, and it can be restarted as often as you like. The Network Monitor expires after 30 days. Turn it into a full version by entering a license key.
Little Snitch 3 and earlier versions that are compatible with previous macOS versions can be found on the following page.Older Versions