Some signs that people may be bored or disinterested in what you're saying:
- Sitting slumped, with heads downcast.
- Gazing at something else, or into space.
- Fidgeting, picking at clothes, or fiddling with pens and phones.
- Writing or doodling.
When you notice that, you can re-engage people by asking a direct question, or by inviting people to contribute an idea.