Notifications are sent to your Host after a visitor has signed in or has signed out. If the Host has an email address configured, an email will be dispatched. If the Host has a mobile number configured, a SMS (text message) will be dispatched. This email and/or SMS (text message) can be configured from the backoffice website as shown below. Signout notifications are only sent out as email notifications.
Note that you can use placeholders in these notifications as described here: https://vizito.be/faq/20-badge-printing/6-which-placeholders-can-be-used