The standard THERMOFLEX™ heat detector connects to a fire alarm system’s input circuit as an initiating device. In heat detectors with Normally Open internal contacts, the contacts will close when the detector operates either on a rate of temperature increase, or if the releasing temperature is reached. In heat detectors with Normally Closed contacts, the contacts will open under the same conditions. The Rate-of-Rise function is recommended in conjunction with sprinkler devices as the detector will initiate and alarm before the waterflow switch.