Monitor and system for monitoring

A system 10 that monitors the well-being of a person comprises subject monitoring 12, carer 18 and control 14 devices each having a communication device. The subject monitoring device comprises a sensor. The control device receives and stores the sensor data in a memory, processes the sensor data according to a first set of rules and determines a status based on the processed sensor data. The status is communicated to the carer device. The subject monitoring device processes sensor data according to a second set of rules and determines an alert if the rules are satisfied. The alert is then communicated to the carer device. The control device can include a unit that controls aspects of the subjects environment in response to a status requiring action being set. A control device may also be configured to receive data input by a user, compare the user input data with the sensor data and process both the user input data and sensor data according to a first set of rules so as to determine a second set of rules. The second set of rules is then used to categorise received sensor data so as to determine a status of the subject.