A monitor allows to supervise certain conditions of a robot during a sequence. Examples could include the following situations:

• A sequence steers a robot along a given path. A monitors checks for obstacles. As soon as an obstacle is close enough, the monitor causes a predefined exception sequence to be executed.
• A sequence takes too long to run due to some erroneous behavior. A monitor checks for timeout and either restarts or aborts the sequence or switches to an exception sequence.
• A sequence moves a robot arm. While moving the arm looses its load. A monitor checks for this load to be present and aborts the sequence.

All these situations have in common, that a user does want to check for a given set of conditions during the running of the sequence (including subsequences or steps).