This is the replacement temperature sensor for the FA-I-CCA, FA-D2 and FA-800E FreezeAlarms and FA-900E TempAlarm only. The 3.5′ length is the version that is normally shipped with these FreezeAlarm models. The sensors feature a nickle plated capped sensor that is not submersible in water. It needs to be placed in a well with insulating putty or other material if monitoring liquids. The sensor has an RJ9 telephone headset type connector that is only compatible with the FA-I-CCA, FA-D2 and FA-800E FreezeAlarm and FA-900E TempAlarm models.