A method of operating a robot including a vacuum port for engaging an item, e.g. a wafer, is disclosed. The method includes operating, by a computer system, the robot in a first state, detecting using a vacuum sensor, a transition of a vacuum parameter from a first vacuum parameter zone to a second parameter zone in a plurality of vacuum parameter zones. Based on detecting the transition of the vacuum parameter from the first vacuum parameter zone to the second vacuum parameter zone, the operating state of the robot is altered from the first state to a second state. Also disclosed is an item transfer robot as part of an item transfer system.