In a HotSOS-integrated environment, the "Checked In" tag is applied automatically upon the reservation being checked in within the PMS. 

Messaging inhouse guests is then as simple as sending a new message to the "Checked In" tag. Create further segmentation by using the "Checked In" tag as part of segment criteria from the Contacts pane. In the example below, we're pulling inhouse reservations that are registered to the 6th floor. 

Additionally, Zings can be used to run actions based on the event of the tag being first applied. A welcome message could be created by choosing "Checked In tag is added" as the trigger and "Send message to contact" as the action.