The reliability of fire alarm systems is required to be much higher than some other building systems, due to the reliance placed on active fire protection systems for life safety. This is a fundamental consideration underpinning the NZ building Code and the associated Compliance Documents. Designs therefore tend to be conservative, based on risk and experience. 

Mains power supplies are expected to fail under fire conditions, so battery back-up is expected. Batteries are known to fail, so are tested almost continuously by the fire alarm system both for continued presence and capacity. Circuits are automatically supervised for fault conditions, producing fault signals in case of failure.
Sometimes wiring circuits are required to be installed with redundant paths. 

Because reliability is so important, monthly testing and annual surveying of fire detection and alarm systems by a qualified trade practitioner is mandatory. Fire detection systems are invariably listed on a building’s compliance schedule, and evidence of satisfactory test and survey must be submitted to the Territorial Local Authority before the building’s annual warrant of fitness (for continued occupation) can be issued.