What do you mean by "checked in"?
erm, made contact.
I was going to put sent events, taken updates or DAT but i'm concious that these might not take place or might fail due to other issues.
As a bit of background, we had a comms issue with a server that just affected its ability to make communication from the server to EPO via the client, DAT level was the first indication we had that there was a problem.
You can monitor this through the dashboard.
If a computer has communicated, if has the lastest DATs, etc.
Though, you can generate a report of machines that are not communicating for the past X days and have it sent to you through email.