A fire system for a building, the fire system comprising: a fire panel for monitoring the building and activating an alarm, the fire panel comprising a loop controller; and a plurality of remote units (14, 16, 18) electrically connected to the fire panel in a circuit having a loop configuration, the loop controller being for controlling operation of the loop; wherein at least one of the plurality of remote units (14, 16, 18) comprises an indicating device for determining conditions that are indicative of a possible emergency and modulating a current in the circuit when those conditions indicate a possible emergency; wherein the plurality of remote units (14, 16, 18) are in communication with the fire panel in a master-slave relationship; characterized in that: the system is configured to enter a degraded mode of operation when failure of the master-slave communications occurs, the fire panel being configured to create a high output impedance in the circuit and enable a degraded communications mode for the remote units (14, 16, 18) in the degraded mode; each of the plurality of remote units (14, 16, 18) comprises a current sensor for detecting current in the degraded mode; the fire panel comprises a supervisor for supervising the loop controller, and the supervisor is configured to create the high output impedance in the circuit in the degraded mode; and the at least one indicating device is configured to encode the modulation in current with alarm information, and, in the degraded mode, the current sensors of at least some of the remote units (14, 16, 18) are configured to decode any detected modulations in current such that the alarm information can be determined. a fire panel for monitoring the building and activating an alarm, the fire panel comprising a loop controller; and a plurality of remote units (14, 16, 18) electrically connected to the fire panel in a circuit having a loop configuration, the loop controller being for controlling operation of the loop; wherein at least one of the plurality of remote units (14, 16, 18) comprises an indicating device for determining conditions that are indicative of a possible emergency and modulating a current in the circuit when those conditions indicate a possible emergency; wherein the plurality of remote units (14, 16, 18) are in communication with the fire panel in a master-slave relationship; characterized in that: the system is configured to enter a degraded mode of operation when failure of the master-slave communications occurs, the fire panel being configured to create a high output impedance in the circuit and enable a degraded communications mode for the remote units (14, 16, 18) in the degraded mode; each of the plurality of remote units (14, 16, 18) comprises a current sensor for detecting current in the degraded mode; the fire panel comprises a supervisor for supervising the loop controller, and the supervisor is configured to create the high output impedance in the circuit in the degraded mode; and the at least one indicating device is configured to encode the modulation in current with alarm information, and, in the degraded mode, the current sensors of at least some of the remote units (14, 16, 18) are configured to decode any detected modulations in current such that the alarm information can be determined. the system is configured to enter a degraded mode of operation when failure of the master-slave communications occurs, the fire panel being configured to create a high output impedance in the circuit and enable a degraded communications mode for the remote units (14, 16, 18) in the degraded mode; each of the plurality of remote units (14, 16, 18) comprises a current sensor for detecting current in the degraded mode; the fire panel comprises a supervisor for supervising the loop controller, and the supervisor is configured to create the high output impedance in the circuit in the degraded mode; and the at least one indicating device is configured to encode the modulation in current with alarm information, and, in the degraded mode, the current sensors of at least some of the remote units (14, 16, 18) are configured to decode any detected modulations in current such that the alarm information can be determined.