Abstract: A monitor apparatus and method for monitoring, verifying, and prompting an existing CO2 type fire suppression system in a room or building protected by the suppression system. In its most preferred form the monitor apparatus is a unit contained in a cabinet or housing placed in the protected room, with only a signal connection to the suppression system. The monitor apparatus has a suppressant gas concentration sensor enabled by a discharge signal received from the suppression system, and a datalogger to keep a verifiable record of the suppression system's discharge performance. The monitor unit sends a continue-discharge signal back to the suppression system independently of the continuity of the suppression system's discharge signal if a desired gas concentration level in the room is not reached or held per the suppression system's own requirements.