Products › F-SENS 1124 – Ultrasonic Air Flow Sensor for HVAC Duct Image 1 of 3 Image 2 of 3 Image 3 of 3 F-SENS 1124 – Ultrasonic Air Flow Sensor for HVAC Duct $378.00 Monitor HVAC airflow with the F-SENS 1124 using patented, reliable, and robust ultrasonic principles. Add To Cart Added! Monitor HVAC airflow with the F-SENS 1124 using patented, reliable, and robust ultrasonic principles.