Apparatus for monitoring muscle activity, said apparatus comprising means for providing signals indicative of muscle activity, for example EMG-signals, means for processing of said signals in order to detect a particular activity and means for providing a feedback signal, wherein said device is designed in order to be individually adaptable in a set-up mode. The apparatus can be used for detecting and prevention of undesired activities such as bruxism, movements that are damaging or unwanted etc. The detection can be performed with great certainty since the individual parameters of the user are utilized for laying down reference values, threshold values, criteria for triggering of feedback signals, etc., which may take place at a set-up procedure.