Protectowire Linear Heat Detector is a proprietary cable that detects heat anywhere along its length. The sensor cable is comprised of two steel conductors individually insulated with a heat sensitive polymer. The insulated conductors are twisted together to impose a spring pressure between them, then wrapped with a protective tape and finished with an outer jacket suitable for the environment in which the detector will be installed.

Type XCR consists of a high-performance fluoropolymer jacket and is designed for exterior environments as well as harsh interior applications. Features of this low smoke jacket include excellent chemical resistance, abrasion resistance, weather resistance, and high-temperature performance. XCR is the only detector that is FM-approved for corrosive environments.