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Honeywell 5821 Wireless Temperature Sensor & Flood Detector


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Honeywell 5821 Wireless Temperature Sensor & Flood Detector

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.


Operating Temperature: 14 F (-10 C) to 104 F (+40 C)
Operating Voltage: 3.2VDC
Dimensions: 3.1" length, 1.6" wide, 1.0"


Sensor Parameters:

Cold Temperature
(Freeze) Detector 45° F (7° C)
Warm Temperature
Detector 75° F (24° C)
Hot Temperature
Detector 95° F (35° C)
Refrigerator Failure
Detector 42° F (6° C)
Freezer Failure
Detector 10° F (-12° C)
Hysteresis 3° F (-16° C)
Flood Sensor inch of water covering the probe
Response Time
Tolerance +50%, -20%
Temperature Measurement
Accuracy (internal temp. sensor
or external temp. probe) 3° F (-16° C)


  • Five selectable temperature ranges to choose from (hot, warm, cold, refrigerate and freeze) 
  • Remote Temperature Probe available (T280R) ideal for refrigerator and freezer monitoring 
  • Flood detection with 470PB External Probe for a wide range of applications; including bathrooms, laundry rooms and basements 
  • Up to 10 year battery life, which reduces user maintenance Completely wireless, which greatly reduces installation time and maximizes placement options 
  • Capable of monitoring cold (45° F) temperature and flood detection simultaneously

5821 Installation manual
5821 Data sheet


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