Heat-responsive devices are either a Linear Heat or a Spot Heat Detection type.
These systems are relatively low cost. They cannot detect small, smoldering fires. Line-type detectors can be installed in a relatively inconspicuous manner by taking advantage of ceiling designs and patterns. (See NFPA 72, National Fire Alarm Code.) The air temperature surrounding a fixed temperature device at the time it operates usually is considerably higher than the rated temperature, because it takes time for the air to raise the temperature of the operating element to its set point. This is called thermal lag.
There are numerous applications where Linear Heat Detection is used such as Refrigerated Storage (Freezers), Warehouse, Bridges, Conveyors, Chemical and Gas Storage Facilities, just to name a few. A fire protection professional can assist you with determining the best application of specialty products like these.