Linear heat detection replaces a point device with a continuous line. In the digital form, two spring-steel conductors are held apart by a heat-sensitive polymer; anywhere along the run that reaches the rated temperature, the polymer softens, the conductors touch, and the loop shorts, giving an alarm without saying much about where. In the analogue and fibre-optic forms, a resistance measurement or a laser pulse launched down an optical fibre returns a temperature profile along the whole cable, with a location resolution of around a metre, using the temperature dependence of backscattered light. That is the deciding feature: this is the detection technology for long, hostile, or inaccessible geometries such as cable tunnels, conveyor belts, tunnels, car park decks, and transformer or battery installations where a point detector could never be placed close enough or survive. The trade is cost and the same thermal lag that afflicts every heat device. After this Concept you can say when a line of detection beats a grid of points, and what a fibre system buys you that a shorting cable does not.
Fiber-optic linear heat detection is an active (continuously reporting) alternative to passive fixed-temperature or rate-of-rise heat detectors, functioning as a distributed thermometer along the ful…