User Activity Monitor : Monitoring Settings : Options : Multiple displays
  
Multiple displays
The Multiple displays option applies to computers with multiple displays, and it allows the administrator to specify whether to record the screen of a single monitor or the screens of all monitors. In the latter case, it is possible to combine all the monitors into one record or record each monitor separately.
Double-click this option to view or change the selection of its setting in the dialog box that appears:
Only the primary monitor - Only the primary monitor screen is recorded.
All monitors as single file - The screens of all monitors are recorded in a single record.
All monitors as separate files - The screens of all monitors are recorded, with a separate recording made for each screen.