If you are looking at the appointment detail record for an appointment that's either in Open status or No Show status, you can change the appointment to "Checked In" from within the Appointment Detail page. To do this, simply select the "Mark As" dropdown and select "Checked In".
Here is what this looks like from the Appointment Detail screen for an Open appointment:
You'll then be prompted to confirm that you really want to mark this appointment as "Checked In". If you do, hit the "Confirm Client Check In" button. If not, you can hit "Cancel" and it will return you to the Appointment Detail page without changing from Open to Checked In.
Once you confirm that you do want to check the Open Appointment in, the Appointment Detail page will update with the change. The new status will read "OPEN | Checked In:" with a timestamp for when the appointment was Checked In:
The same logic applies for when you are marking a No Show appointment as Checked In. This may happen if you have waited for several minutes for a client to come for his/her appointment and after a certain period of time, you mark them as No Show. If they show up after that, you can mark them as Checked In from the Appointment Detail record of that No Show status appointment. You'll simply access the "Mark As" drop down menu and select "Checked In":
You'll receive the same prompt as before, only this time after pressing "Confirm" you will see the status change listed in the Audit Trail that it went back to "Open Status".
Appointments can also be marked as Checked In from the Open Appointments list view. To find this view, go to Appointments → Appointment Lists → Open. Select the appointments that you want to check in using the check boxes next to their listing in the displayed table then click the "Check In" button:
The Check In confirmation modal will appear and you can select to Confirm you want to check the clients in:
Once you confirm that, the screen will refresh and show you the Checked In appointments list:
It may not be a frequent thing that you're marking No Show appointments as Checked In, but it's worth noting that it's indeed possible to do. Why might you have to? As mentioned above, you may have waited for several minutes for a client to come for his/her appointment and after a certain period of time, you mark them as No Show. If they show up after that, you can then mark them as "Checked In" without having the Re-Open the appointment to do so.
To do this from the No Show list view, go to Appointments → Appointment Lists → No Show. Select the appointments that you want to check in using the check boxes next to their listing in the displayed table then click the "Check In" button:
The Check In confirmation modal will appear with a summary of how many appointments you are checking in. You can select to Confirm you want to check the clients in or Cancel if you don't want to check them in:
From here, the screen will refresh and you will see the Appointment listed in both the "Checked In" list as well as the "Open" list, as Checked In is a sub status of Open.
If you want to see all the appointments you have Checked In at any given time, you can look at the "Checked In" appointment list. To do this, Appointments → Appointments →Appointment Lists → Checked In and customize the Date Range for the dates you want to see your Checked In appointments for (this will typically just be today, as we're sure you'll go through and complete/check out your appointments once they're finished 
):
You can click the View button next to the appointment record in the List to go into it's Appointment Detail page. From here, you can also change the appointment status to "Completed" or "No Show" or remove the Checked In substatus by "Re-Opening" the appointment.
You can also tell which appointments are Checked In from the "Checked In?" column on the Open Appointments list. This way, you can see your Open appointments for a day as well as who is currently at the office:
