Indicator devices and systems for explosion-proof enclosures are described. The indicator devices include a sleeve coupled to a dome-like transparent member by a connector body, at least one conductive contact positioned in the sleeve, a piston responsive to an increase in pressure and positioned in the sleeve, and an indicator. The indicator can be a light source positioned in the transparent member or an alarm external to the indicator device. Upon an increase in a pressure in an enclosure to which an indicator device is attached, the piston shifts and contacts the at least one conductive contact and permits the completion of an electrical circuit from a power source to the indicator. The indicator systems include an indicator device coupled to an explosion-proof enclosure.