The Honeywell 5821 is a multi-purpose wireless sensor. By itself it can be used to sense either a rise in temperature or a lowering of temperature in the location where it is installed. It has five different temperature settings that can be detected. This sensor also has add on probes that you can use. One is a T280R which lets you monitor freezer or refrigerator temperature. The other probe is the 470PB which will convert the 5821 into a flood detector. The 5821 can be used multiple ways and is a must for those who worry about freezing or floods.