When using the site management QR codes you can see who's scanned the code and “Email All”. This can be useful if you need to notify everyone that is on site for something. 

To Contact everyone who is signed into a Site:

1. Navigate to the Performance Dashboard.
2. Click ‘Site Management’ from the left panel.
3. Click into the Site.
4. Click ‘Export’.
5. Click ‘Email All’

(note you will need to have an email service on your device)