Review: Aqara indoor climate sensor (for home automation)

The Aqara Temperature and Humidity sensor by Xiaomi (ad: available on Amazon) is a popular option to capture indoor climate data for home-automation systems. The sensors are small, plainly designed, cheap, promise 2-year battery life, and run on the Zigbee mesh-network protocol. However, they’re also notoriously unreliable, which defeats the desired set-it-and-forget-it target for the sensor.

I had to lower my expectations of the sensor after unboxing and skimming through the user manual. The manual says that the sensors don’t work in high-humidity environments (like a bathroom, basement, or refrigerator). The sensor isn’t suitable for use in fridges anyway, as they’re essentially faraday cages that block wireless signals. This limitation was quite unexpected. The sensor is unfit for its primary marketed purpose: it’s supposed to be a hygrometer!

The Aqara sensor communicates over the industry standard Zigbee protocol, and it should work with Zigbee hubs and devices from many different vendors. The Zigbee protocol will soon be rebranded as Thread for Matter. The new unified industry-wide standard for the internet of things (IoT). The Zigbee protocol shares, and thus interferes, with the same 2,4 GHz band as Wi-Fi. However, Zigbee devices maintain a separate mesh-powered network and don’t have access to my more security-critical Wi-Fi network.

Aqara states that you’re required to pair the sensor with an Aqara Hub (sold separately). Aqara doesn’t claim that it’s sensors are compatible with other hubs and controller devices. However, everyone buying these intends to use them with other home automation systems like Home Assistant. I’ll get back to this point in greater detail in the review.

I’ve bought three Aqara sensors for use around my home, so I’ve had the opportunity to compare them to each other and other reference measuring tools. I don’t have any scientifically calibrated thermometers or hygrometers. However, I have half a dozen, and they all agree with each others readings.

The Aqara sensors’ temperature readings are very consistent. When placed right next to each other in temperature ranges between 13 and 29,4 ℃, they stayed within 0,3 ℃ of each other. At 25 ℃ all three sensors show on average 0,7 ℃ higher than my other reference thermometers.

This difference is to be expected for a sensor of this type, and it’s likely caused by the heat generated by its internal electronics. Read Many indoor air quality sensor products are a scam by William Hales for details. The sensors are designed with a small air intake at the bottom facing down toward the floor. Heat raises, so this doesn’t help heat escape efficiently.

I’m more uncertain about the reliability of the hygrometer; accurately measuring relative humidity (RH) requires accurate temperature measurements. My three sensors’ RH readings are within 2,9 % of each other. The sensors that measure higher temperatures consistently report lower relative humidity. Their RH readings would probably be closer if I could correct them for the temperature difference. However, the sensors’ RH readings are 9–16 % higher than my two reference hygrometers. I’ve got one analog and one digital hygrometer, and their RH readings are within 2 % of each other. Aqara errs towards higher RH at higher temperatures.

The temperature readings are good enough for use as a data point for home automation. I wouldn’t rely on the RH readings without normalizing them based on data from a better reference hygrometer. You might be able to configure this through scripting in the home automation hub of your choice.

The sensors have been unreliable in my experience over four months with them. They stay connected to my local Zigbee network and keep sending low-level network traffic. However, they eventually stop sending new sensor data.

All three sensors worked flawlessly for the first three weeks. However, now they won’t stay connected for more than a few days, though never less than 42 minutes. I have not worked out the significance of the 42-minute time window. It’s the shortest and most common duration the sensor will continue to send data after having been re-paired to the Zigbee network.

I have to re-pair it with my Zigbee controller to get it to begin sending sensor data again. Pulling and reinserting the battery does restart it, but a restart isn’t enough to get it to send new readings.

The problem seems worse when the sensor’s battery voltage drops below 3,06 volts. It’s powered by a regular 3 Volt CR2032 coin battery, so the sensor should definitively work at and even quite a bit below 3 V. New 3 V CR2032 batteries start at 3,0–3,4 Volt. The voltage decreases to 2 V toward the end of their life.

I’m notably not using “required” Aqara Hub. I’m using another brand of Zigbee controller. I use the zig-a-zig-ah! (CC2652R) from Electrolama with, as you might have guessed, Home assistant. That being said, the Aqara sensors work just fine with my controller until they eventually decide to stop sending more readings.

There’s plenty of online discourse about the unreliability of the Aqara sensors. People even describes the same problem with the Aqara Hub, as well as with other hubs and controllers. A Zigbee hub is a Zigbee controller that acts as a network gateway between your local Zigbee and Ethernet/Wi-Fi network. So, you can think of a Zigbee hub as an app-controlled Zigbee controller. In my opinion, adding an Aqara Hub to my setup would only add complexity without improving the sensors.

Most people in these discussions believe their sensors get disconnected from their Zigbee mesh networks. These observations don’t match my experiences. I’m unsure if others don’t know how to check if their sensors still communicate with their Zigbee mesh networks.

Whatever the reason, the sensors stop working over time. They require you to periodically re-pair them with your Zigbee controller, and often swap their almost-full batteries too. The Aqara climate sensors are not a set-it-and-forget-it for two-years solution for your home automation needs.

It’s incredibly misleading to market a product clearly intended to be a hygrometer that can’t be used in humid environments. They’re unfit to keep track of the humidity in rooms or environments where that capability would be the most useful. The Aqara sensor can still be used to control home heating and monitor typical indoor climate. Assuming you can get it to keep transmitting sensor readings, of course.

I’ve reviewed the Aqara Temperature and Humidity sensor model WSDCGQ11LM. This is the model you can still expect to find in stock everywhere. There’s also a newer WSDCGQ12LM (lightly branded “T1”) model available that is slowly replacing old inventory. There are many reports of problems with the newer models too, though.