Firelite Heat Probe

Series 302 heat detectors are designed for use in normal
environments as well as environments where the detectors
are subject to weather, moisture (internal condensation), and
explosive atmospheres. They are normally-open devices designed
to close an electrical circuit upon activation. All models feature
rate compensation and are available with either 135F (57.2C) or
194F (90C) ratings. They are self-restoring, hermetically sealed,
shock and corrosion resistant, and are tamperproof.