A system for monitoring a validator that assesses a token includes an input device 4 for receiving messages 5 from a machine 2 including a validator 6. The messages contain data indicative of validator events such as an assessment of a token resulting in acceptance of the token and an assessment of a token resulting in rejection of the token. The system further includes a processor 7 for deriving timing information for the validator events and for comparing the data and timing information with predetermined criteria. Personnel alerts are raised when predetermined criteria are satisfied, and maintenance of validators may be scheduled in dependence upon criteria related to assessments of tokens resulting in rejection.