Abstract: A missing hole detector to detect a missing or misplaced hole in a (e.g., sheet metal) workpiece. The missing hole detector is preferably located at a punching station within the upper turret of a CNC punch press. A pushing force generated during the downstroke of a ram causes a test probe of the missing hole detector to move towards the workpiece under test. A switching circuit connected to a transmitter is responsive to the movement of the test probe. If the test probe is moved into a hole so as to penetrate the workpiece, the switching circuit is opened and the transmitter is disabled. If the test probe is otherwise moved into contact with but fails to penetrate the workpiece because a hole is absent or misplaced, the switching circuit is closed and the transmitter is energized. The transmitter now transmits a stream of data by way of an RF wireless communication path to a receiver.