The disclosure relates generally to devices, systems and methods for measuring, transmitting, recording and displaying information relating to physical exercise and, more particularly, to a monitoring system for monitoring exercise machines comprising a lifting mechanism for selectively engaging one or more of the weights. A first aspect of the disclosure relates to an exercise machine monitoring system for monitoring exercise machines, where the exercise machines, comprise a plurality of stacked weights, the monitoring system comprises, for each of the exercise machines a repetition detector and an exercise machine identifier. The monitoring system further comprises an observer and a user device.