A thermostatic detector is primarily sensitive to which environmental condition?

A thermostatic detector is primarily designed to sense changes in temperature. This type of device operates based on the principle that as the ambient temperature rises due to heat from a fire, it will trigger the detector. The sensitivity to heat makes it effective in detecting the presence of a fire before there is significant smoke or other indicators present. Other environmental conditions such as smoke, sound, or light are not the primary factors for the operation of a thermostatic detector, which is why those options would not be correct in this context.