When presenting a talk, you can send a message to all live attendees by clicking Announcements on the right-hand side panel.
Simply type in your message, click Display announcement, confirm, and your message will be displayed to all live viewers. You can use announcements to remind your viewers to submit questions, notify them of uploaded attachments, announce upcoming or related talks, and more!
NOTE: Announcements are available starting 5 minutes before scheduled start time and throughout your live talk. Only one announcement can be displayed at a time with a maximum of 1,000 characters.