Unable to set offsets on SONOFF temperature and humidity sensor

Configuration
1

I have the cheap SONOFF Dongle Lite MG21 (USB) and a dozen SONOFF SNZB-02WD temperature and humidity sensors, all working fine, and want to set some calibration offsets.

When I tried this, at first I was using the UI with a slider in HA which was very hard to set a value, but I did manage to set - incorrect - values on a couple of sensors. Once I found the UI where I can input the numbers using the keyboard I thought fine, I’ll just fix those and also set them on the other sensors.

Silly me. :rofl:

Since then, whenever I try to change the offset using either the slider or keyboard UIs, it fails and a message pops up (see log extract below). From memory, being able, and then no longer being able to set the offsets happened during a single session using the two UIs so I don’t think there were any other changes to cause this.

Any idea why this has begun happening and how to fix?

Logger: homeassistant.components.websocket_api.http.connection
Source: components/websocket_api/commands.py:334
Integration: Home Assistant WebSocket API (documentation, issues)
First occurred: July 25, 2026 at 3:25:48 PM (42 occurrences)
Last logged: July 26, 2026 at 2:43:27 PM

[140243710547968] Error during service call to number.set_value: Failed to send request: device did not respond
[140243559656128] Error during service call to number.set_value: Failed to send request: device did not respond
[140243810742848] Error during service call to number.set_value: Failed to send request: device did not respond
[140243706778208] Error during service call to number.set_value: Failed to send request: device did not respond
[140243786287840] Error during service call to number.set_value: Failed to send request: device did not respond
2

They’re battery devices - you have to press the button on them to wake them up immediately before setting the new value (like within a couple of seconds).

I’m surprised you managed to set the values without waking up the device in the past. You were either very lucky, or else you did it a short while after pairing.

3

Thanks, I’m not sure that’s right - they don’t have a button - but I can try removing the battery as there have been no other suggestions. I don’t understand why they would be designed to work like that but obviously you could be right.

A better solution would be if I could set the offset in HA somehow. How would I do that?

4

Battery devices sleep most of the time to preserve battery. They only wake up briefly to send sensor updates. If they don’t have a button then you could try to blow on them so they detect the humidity change & wake up to report.

Probably via a template sensor, though I can’t help with that. Personally, I’d avoid creating another sensor when the device has the ability to calibrate already, but you do you

5

Ok useful thanks. What a palaver!

EDIT: Thank you @ShadowFist, breathing on them does the trick. :rofl: I doubt that I’d have figured that out myself.