HomeHome AutomationIs it good? Sonoff SNZB-02D sensor

Is it good? Sonoff SNZB-02D sensor

Another Sonoff in Home Automation town

ITEAD is releasing a new temperature and humidity sensor. It will complement the existing collection of ZigBee sensors in their ecosystem. The main selling point is the LCD display, however, I decided to dig deeper and find out how good the Sonoff SNZB-02D really is. Last year, I tested 11 different ZigBee temperature and humidity sensors, so it’s only fair I’ll take the new sensor and see how it stacks against others.

Sonoff SNZB-02D temperature and humidity sensor

I actually prefer sensors with displays, as it removes the hassle of checking various apps or dashboards to get the basic temperature readouts. I have an affinity for e-ink displays, but these are relatively expensive (Aqara TVOC) so the inclusion of the LCD display seems like a sensible compromise between usability and price. I own several other sensors with displays from Shelly, Tuya and now from ITEAD. At $12.99, Sonoff SNZB-02D it’s a very attractive gadget to have in your smart home.

The design of the sensor is pretty clever. These are small design choices with a meaningful impact. Sonoff SNZB-02D is relatively thin even with the magnetic base attached to it. The base comes with a 3M tape, to wall-mount the sensor anywhere you wish, and once removed from the cradle use internal magnets to stick the sensor to a fridge or retract the stand to support the screen for more standalone use.

It’s an efficient approach, especially, that slanting your LCD screens can aid readability. Other designs like Aqara TVOC or the first SwitchBot relied on the thickness of the base to keep the screen standing.

Just like other Sonoff temperature and humidity sensors Sonoff (SNZB-02), the gadget is powered by a single-cell battery (CR2450) which will keep the sensor in operation for months at a time. I wish there was a slot for a second battery considering the free space inside the enclosure.

The LCD screen displays the temperature (-9℃ – 60℃) and humidity (5-95%) alongside the battery and range indicators. The temperature is also available in Fahrenheit if you are into less SI ways of measuring things. Additional icons for frosty/dry/wet/hot conditions are also available.

Shop with Sonoff

Take a look at the ZigBee and WiFi range of the devices compatible with eWeLink:

Inside Sonoff SNZB-02D

The first step was to open it up and check what the Sonoff SNZB-02D was made of. We know it uses ZigBee 3.0 protocol to communicate with the Sonoff ZigBee hub (or other hubs for that matter). The IC responsible for communication with the hub is EFR32MG22 a familiar Gecko chip which is an improvement from CC2530 IC found on the older Sonoff SNZB-02 Temperature and humidity sensor. I wasn’t able to find any information if the IC that would support the Thread protocol used by Matter.

Temperature and Humidity are measured with 0.2% and 2% accuracy respectively thanks to SM60 series sensors – again a new hardware compared to the previous model.

Data

Current Temperature and Humidity are available in the eWeLink app and updated every couple of minutes or on a sudden change. You can respond to temperature changes with your Automations, but historical data is saved in hourly instalments. This makes it harder to track past usage for heating systems and similar applications. If you require a detailed history, you could use eWeLink API to extract the values on a more regular basis.

In the eWeLink app, the sensor looks identical to the Sonoff SNZB-02 sensors without the display. The only difference can be found in the sensor’s setting where you can set the comfort settings. Setting these values will define when icons for hot/cols/dry/wet icons will appear on the display. Additionally, temperature and humidity alerts are available in case you want push notifications when it gets too hot/cold/humid or dry.

Accuracy

From testing many sensors over time, I quickly discovered that the accuracy of these is pretty spot on. They all report values within 0.5℃ from each other and the accuracy discrepancies have more to do with an airflow and vent design than issues with the sensor.

Running Sonoff SNZB-02 next to my Aqara TVOC reported almost the same values. The recorded difference was within 0.5℃ of each other with humidity reporting less on point. As the sensor assumes 2% accuracy, it’s normal to see values 4-5% apart and indeed that was the case with my Sonoff SNZB-02.

Other ecosystems

If eWeLink is not your ecosystem of choice, I have some news. I tried to pair the sensor with the Tuya hub (Zemismart) and that was successful. The sensor had reported temperature and humidity correctly, but I had no information about the battery and I couldn’t change the units.

I tried the same with Aqara M.2 hub, but this time around the hub flat-out refused to add the accessory. It seems that your experience will depend on what ecosystem you have at home.

Sonoff SNZB-02D with ZigBee2MQTT

The next step is to evaluate the sensor in NodeRED with my custom ZigBee coordinator. I’m using Sonoff Dongle as my coordinator and saving the stats thanks to my Grafana and InfluxDB integration.

Technically, Sonoff SNZB-02D isn’t supported, but the original Sonoff Temperature and Humidity sensor (Sonoff SNZB-02) is, so instead of trying to add a new external converter, I simply added the model number Sonoff SNZB-02, to the existing converter. Both sensors deliver exactly the same payload:

The flow is rather silly, so I’m going to skip to the payload and the data analysis. Here is the data gathered for the last 12h of measurements:

#sample payload
{"battery":80,"humidity":86.9,"linkquality":174,"temperature":16}

From the graph we can deduct the following behaviours:

  • with constant temperature/humidity sensor reports back approx once every 20 min
  • The update threshold appears to be 0.2℃ – a change in the temperature bigger than this threshold triggers an instant update
  • response to changing conditions is about 5 sec
When blown upon the sensor

In summary, the sensor in low power states drops updates to 3-4 per hour given the lack of atmospheric changes and is capable of updates at the rate of 6 updates per minute when placed in a volatile environment.

As this is a brand-new device, I can’t comment on the battery life. The use of CR2450 is promising as the bigger capacity battery means longer runtime. Time will tell how long the battery can keep the display and the sensor operational.

Final thoughts

Sonoff SNZB-02D is an excellent budget sensor and if I could change anything about it, would be the ability to retain the data inside its hardware just like SwitchBot does. Other than that you have my genuine recommendation for both: use with eWeLink and custom systems like NodeRED. Let me know if you have any questions about it in this Reddit thread.

🆓📈 – See the transparency note for details.

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