Thermal mass sensors by Innovative Sensor Technology utilize heat transfer principles to determine the flow velocity of a fluid. These sensors are applicable in both gas and partially in liquid, are able to detect the presence of a liquid, biofilm, or bubbles, and can indicate liquid level.  Gas flow products include more sensitive units such as the MicroflowSens and MFS02, both featuring 0.0001 m/s sensitivity and <10 ms response time, to products with broader measuring ranges, such as the FS2 and FS5 that measure up to 50 m/s and 100 m/s, respectively. There are also four liquid flow models, each offering a measuring range from 0 to 10 m/s, sensitivity of 0.01 m/s, and response time <100 ms.

Gill Sensors produces ultrasonic flow sensors that are suitable for harsh environments, which take measurements in both directions and use difference in the time of flight to calculate flow velocity. Available products include the mass airflow sensor, which is capable of measuring bi-directional flow up to 600 kg/hr with a resolution of 0.001 kg/hr and turn-down ratio >1,000:1; and also a medical gas flow sensor for anesthesia and ventilation monitoring, which provides a flow range from 0.2 to 150 l/min, accuracy +/-3%, and resolution of 0.01 l/min.