> Yes, you can use database level on connect/on disconnect triggers. E.g.

FYI, one problem of this solution is that in case of a server crash / power outages the on disconnect trigger is never called. The same happens when a connection is killed by another user (DELETE FROM MON$ATTACHMENTS ...). So there must be another mechanism that cleans the CONNECTED_USERS table in such cases. At least in FB 2.5 where I tested it.

Regards, Michal