Monitoring means the printer's status gets read (periodically) in order to be able to report the printer's state to a user. Think about the paper tray is empty and needs to be refilled. The paper tray can be empty while a new printing job should start or it can be empty while already printing. Thus, it makes sense to monitor the printer's status periodically.

But the world isn't perfect and some printers are in trouble if you retrieve their status too often. There are known printers in the field, where a status read destroys the printer's buffer content which makes the print fail.

Section	Variable
features	monitor

Values:

always
never
idle

always

Monitor the printer device:

when idle
prior sending the printing data for each page

never

Never monitor the printer device.

idle

Monitor the printer device:

when idle

This setting can control how to monitor the printer. A printer which is perfect can live with the always setting. In this case it gets monitored even in idle state. Some printers report their transition into the power save mode while idle for a long period of time. With always this transition will be reported to the printing coordinator and can be retrieved by clients. With this setting an empty paper tray will be reported immediately. The same is valid for all kind of paper jam or other types of errors which can happen at the printer's side while printing.

The never setting is the opposite of always. With this setting there will be no disturbance of any printing activity, but no status reports for clients as well. Even if the paper tray is empty, there will be no warning for a client about this fact.

Some printers are in trouble only if they currently are printing when their status should be read. With the setting idle monitoring is restricted to the idle period only. Monitoring is stopped prior the printing of the first page and continued after the last page was printed, e.g. the next idle period is started.

If this setting isn't made, the default behaviour is always: the printer is expected as perfect.

If an invalid setting is made instead, it defaults to never to be safe.

You can add this INI setting into

the dedicated printer INI in its CAPS Printer Device Parameter Directory
a driver specific INI file in the CAPS Printer Driver Configuration Directory (for all printers using this driver)
or in capsdriver.ini in the CAPS Printer Driver Configuration Directory (once for all printers)

For what events are monitored refer the internal function caps_drv_printer_check().