Resistance thermometer THERMASGARD® RSTF with passive output, in an elegant enclosure made of plastic, with snap-on lid, based with 4-hole attachment, for installation on vertically or horizontally installed in-wall flush boxes, with predetermined breaking point for on-wall cable entry, which is specifically used for temperature detection in larger rooms. The room radiation temperature sensor RSTF determines the effective portion of active radiation or the effective radiant heat at the measured location. Due to the measuring method employed by the dark radiation sensor, an excellent measuring result that is representative of the room is achieved.