When you are logged in at https://app.trylobbyfox.io/, you can see a list of the visitors who are currently checked in at your office.
Click on Visitor Reporting > Visitors to see the following screen:
Here, you can view individual visitors' profiles, which highlights their check in/check out history. You can also send them a text message by clicking the speech bubble icon. If you need to send EVERYONE a text message for any reason, you can do so by clicking the SMS BLAST button towards the right of the screen..