These smoke pencils are battery operated smoke sticks. A very small internal heating element heats the Glycerine, Glycol & Water solution to produce a fine steam that looks like smoke. The smoke is non-toxic, smells faintly sugary and is of a good consistency for draught testing.
The smoke density and duration are easily controlled by a progressive trigger. Being produced electrically, smoke is always available on demand. There is also a built-in LED light that helps to illuminate the area you are testing. Batteries last a long time, 1400 mAh or better NiMH rechargeable batteries are recommended.