Alarms are identified by the instrument if a self-test parameter goes beyond the range of a user-defined or manufacturer-defined setting.
Examples of manufacturer-defined settings include temperatures and circuit power. Alarms arise when a fault is identified that prevents measurements from being taken.
User-definable alarms include tilt-angle and lead-acid battery shut-down voltage. If the ceilometer senses that these are out of range, it will report alarms in the message string, as well as in the Alarm Flag section of each message.