Most fatal fires are found by smoke long before there is any heat to feel, which is why the smoke detector is the device that does the most work in a building. An optical chamber watches for particles scattering light and raises the alarm while the fire is still smouldering.

Revere sets out detectors to the spacing and ceiling heights the code requires, avoids the airflow paths that cause false alarms, and logs every device so a fault can be traced to a room rather than a zone.