Designed for use with either standard Siemens Fire Safety systems or other commercially available fire alarm systems, the Detect-A-Fire Explosion Proof Thermal Detectors are of the rate compensated type. The detector element in all models is self-restoring after operation. Feauturing models in a wide range of settings, the Detect-A-Fire explosion proof models can be supplied with Normally Closed contacts at 140, 160, 190, 210, 225, 275, 325, 360 or 450°F settings or with Normally Open contacts at 140, 160, 190, 210, 275, 325, 360, 450, 500, 600, or 725°F settings. Factory Set and Hermetically Sealed in Factory Set and Hermetically Sealed in a Stainless Steel Shell, these detectors are only explosion proof when mounted in an approved explosion proof junction boxes. UL Listed, and FM Approved as Fenwal Model Series, 27120 and 27121 Manufactured for Siemens Fire Safety by Fenwal.