The mechanical frost protection thermostat / frost monitor THERMASREG® FST with switching output, fully active sensor rod, with automatic reset or with mechanical interlock and manual reset, is available with capillary lengths of 0.6 m, 1.8 m, 3 m, 6 m or 12 m. This frost protection monitor is used for monitoring the air-side and water-side temperature in heat exchangers, water circulation systems and heating registers to prevent frost and avoid frost damage, e.g. in ventilation and air conditioning ducts. All devices are self-securing with sensor break detection.