Handheld: Diffusion
What is a diffusion gas detection device?
When individuals look to purchase a portable gas detection device that measures by diffusion, this is just a term meant to determine its detecting method.
With diffusion gas detectors, they work when the sensor is exposed to the ambient air (often protected by a dust/water filter) and will measure the target gas by means of the diffusion principle.
Diffusion means the proportional spread of molecules over the available space; from high concentration to low concentration.