A method of generating an alert message, the method including the steps of: a) inputting a location identifier into a communication unit; b) transmitting the location identifier from the communication unit to a central monitoring station; c) receiving the location identifier at the central monitoring station; d) retrieving information associated with the received location identifier from a database; and e) outputting an alert message which varies in accordance with the retrieved information. And also a method of generating an alert message including the steps of: a) storing one or more schedule records, each schedule record including a time range and associated schedule information; b) receiving a duress message from a remote communication unit; c) determining a receipt time of the duress message; d) selecting a schedule record having a time range which incorporates the receipt time; e) retrieving the schedule information from the selected schedule record; and f) outputting an alert message which varies in accordance with the retrieved schedule information.