A hygrostat is an instrument that measures and regulates the humidity levels of a space. There are several synonyms for this word including humidistat, moisture controller and humidity regulator. Another term that can be used in place of hygrostat is a dehumidistat, which is a device that controls the amount of moisture in the air by turning on and off the dehumidifier. Other common terms that can be used to describe a hygrostat include humidity gauge, moisture indicator and humidity sensor. Regardless of the term used, all of these devices perform the same function of regulating the moisture content in a given environment.