Regulators refer to devices that control the flow, pressure, temperature, and voltage of either current or fluids in an engine of a car. It may also refer to the opening and closing of power operated window and doors. Regulators are used in many different systems in a vehicle. They are used in the engine to control voltage and currents in many different electrical systems in the engine and other components of the vehicle. They are also in frequent use for all hydraulic systems in a vehicle. Some of the systems that use regulators include auxiliary air, crankcase, exhaust, fuel, alternator, oxygen/air intake, among many others. Many pressure valves also act as regulators to many different systems. Windows and doors operated by electricity use regulators to ensure that the proper amount of voltage is used and that the signals for up and down, open and shut are instigated when asked for.