The CF135W is a fixed temperature only detector. The fixed temperature portion consists of a spring-loaded plunger retained by a fusible alloy that releases when the ceiling temperature reaches 135°F (57°C). When released, the plunger strikes a normally open set of contacts and holds them closed. Spacing on an uninterrupted ceiling is 40’ (12.5m). The CF135 is identified by a black dot on its heat collector fin.