The Sensata Dominican REP (or Mexico depending on where made) RP13A is a thermal protector* for lighting fixtures. It has a dedicated voltage 120Vac. The RP13A has high sensitivity and has three leads, black, white and blue. When the temperature of the fixture is exceeded it will cause the light to blink. It is auto resetting for when the fault is corrected. The Sensata RP13A is designed to fit into a 1/2" KO.
*A thermal protector is a safety device designed to prevent lighting fixtures from overheating, which can lead to damage, fire hazards, and reduced lifespan of the fixture.