ULV (ultra-low volume) foggers, also called cold foggers, don’t use heat. Instead, they produce fog using pressure in one of two ways: Either the insecticide solution is pumped through a high-pressure nozzle or the solution is slowly sent through a vortex of high-speed air. The pressure breaks up the liquid into tiny droplets, which then spray out as an invisible fog. The motors are typically powered by either electricity or batteries but some models use gasoline. Operators can adjust the size of the droplets produced by ULV foggers, allowing for different uses. The lack of heat (and thus fire risk) makes ULV foggers safer for indoor use.