Guardian 500 Airflow Monitor senses and alerts the operator to low airflow conditions. Includes a face plate with circuit board, electrical power pack, vinyl tubing and airflow tube adapter. From the monitor's face plate, the user can easily select and calibrate a set point between 30 and 250 fpm using a velocity meter and a screwdriver. A green LED glows to indicate "safe" when airflow is greater than the low set point. A red LED flashes to indicate "low when airflow is below the low set point. An amber LED flashes when the sash is raised above the maximum safe working opening height. An audible alarm sounds (and can be muted) when under "low" and "sash high" condition. Includes night setback, external alarm and alarm mute functions.