The detector shall be either a single circuit or a dual-circuit type, normally open. The detector shall be rated for activation at either 135 or 194 °F and shall activate by means of a fixed temperature thermal sensor or a combination fixed temperature or rate of-rise thermal sensor. The rate of rise element of combination fixed temperature or rate of rise models shall be restorable, to allow for field-testing. The detectors shall include an external collector that shall drop upon activation to identify the unit in alarm.