An unusual style of a classic device used in countries plagued by mosquitos. When in use it releases a tiny amount of pyrethrin in an oil carrier, that isn't enough to kill insects, but will cause them to go out of biting mode. That's an important thing when mosquitos cause an estimated 700,000 deaths a year globally.
The origin of pyrethrins is fascinating and has a very long history. It was first noticed that a particular plant was good for keeping insects away from other plants in the vicinity. It's a variant of the chrysanthemum family of plants, and initially a pesticide was made by drying the flowers and crushing them to make a powder, but later evolved to creating an oil/resin that could be emulsified with water or mixed with oil.
Once the chemistry was understood, a number of synthetic versions were made to allow easier production. This unit uses a small (0.6%) amount of cypermethrin dissolved in a refined oil carrier like isoparaffin or kerosene. It evaporates so slowly that each 45ml bottle is quoted as lasting up to 300 hours - or a month of nightly use.
Unlike aerosol insect sprays that put out a concentrated burst with the intent of deactivating insects completely (fly spray), this style of unit puts out only enough to trigger a defence response in biting insects that stops them biting. Mosquitos can detect a quantity of as little as a few parts per million in air, and that is enough to deter them and make them try to leave the area.
Although the pure liquid does pose a risk of toxic effects to larger mammals like pets or humans, the small amount of vapour poses virtually no risk. However, the units should not be used in very small enclosed areas with poor airflow.
The plugs used to vaporise the oil are usually rated 2 or 3 watts as that is all that is needed to give a controlled amount of vapour. The low power means that many now use a USB power source, which makes the units smaller, lighter and safer.
An interesting note about the Indian (Good Knight) version is that the added floral aroma did give confirmation that the vapour was diffusing throughout the room.
If actually travelling somewhere that mosquitos are a genuine risk, then I recommend only buying a reputable brand of liquid or one-night tabs from a trusted source. Unfortunately that rules out the usual online suspects. Also keep in mind that the ultrasonic units are worthless and the "UV" insect traps do not attract mosquitoes, as they are following your scent and the carbon dioxide in your breath.
The QR code on the Chinese bottle linked to this data page:-
http://zsewm.com/21701501000000000000000123456944
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