An electronic device called a flow sensor detects how fast a fluid (liquid/gas) is moving through a pipe (duct/channel). It will detect the movement of the fluid, change the flow rate into an electrical or digital signal so that monitoring, recording and control of the process can be done automatically.

Flow sensors work differently depending on how they measure the air/water for example, a mechanical rotary device (watch) has a five minute timer at 12 on its dial (clock face).

The flow sensor may be using: 

- mechanical rotation
- thermal transmission
- electromagnetic induction
- ultrasonic (sound) waves
- Differential pressure

The technology you choose will depend on what type of fluid you are using and how accurately you want to measure the flow rate as well as your ambient conditions. Flow sensors can be built to measure either volumetric or mass rate in addition to detecting the existence of flow. Today's flow sensors are small, rugged, very energy efficient, and are typically capable of transmitting data in real-time and will work with other devices such as IOT's, industrial control systems and automated monitoring systems.

Flow sensors are used in almost every industry where you need to measure fluid flow rates and add systems, this includes; manufacturing & processing, HVAC, Collection and Treatment of Water/Wastewater, Chemical Processing, Medical devices and Smart Buildings.