Access to the admin tool is managed by database level permissions and system functions for specific features and menu options.
Whilst there's no general system function allowing access to the admin tool, it's possible to query which workers have logged in by querying the MO_SESSIONS table in the Mosaic schema where the field IMPLICIT_LOGON equals Y.
The following queries are useful:
select * from MO_SESSIONS where IMPLICIT_LOGON = 'Y' order by logon_datetime desc
select * from MO_SESSIONS where IMPLICIT_LOGON = 'Y' order by last_activity_datetime desc