Hobbs Switch. Boost Activated, Boost Level Adjustable.Commonly used for automatically turning on secondary items such as additional injectors, intercooler misters, water injector, nitrous.The popular boost sensitive “hobbs” switch features 1 wire switching to turn on secondary devices such as additional injectors, intercooler misters, water/alcohol injection, or nitrous.The unit has two additional unique features:1) Standard 1/8NPT style pressure port for universal use.2) Boost trigger level adjust (4-25 psi) via the top allen screw.