1. To create an unlisted hangout on air (HOA), go to the G+ app and click Hangouts, then "Hangouts on Air" to start a new HOA.
2. To make the HOA unlisted, delete the "Public" audience and type the names of people you want to invite in the audience space. Only invited users will receive a link to view the unlisted broadcast.
3. You can start broadcasting now or schedule for later, choosing date, time, and duration. Then click "Share" to email invitations. Invited users click a link to watch.