Can anyone recommend a humidity sensor that's accurate? I'm also looking for a smart plug that shows energy consumption on a dehumidifier that'll talk to the humidity sensor for on and off operation. Thanks.
I have several of these:
They're very responsive, reasonably accurate, and work with Hubitat. The only caveat is that they're restricted to zigbee channels 15, 20, and 25.
I have a couple SmartThings zigbee outlets that I use for power monitoring, but I don't know if they're rated to handle the high influx current a dehumidifier is likely to have when the compressor turns on. Zooz has an outlet that may be more appropriate for this use.
I have a bunch of these
I don't know how accurate they are but they are consistent and very responsive plus the driver allows you to enter an offset value to make it read what you wish.
These are terrific sensors. I use mine mostly for temp and illuminance.
What’s your idea of accurate? For the use case you’re describing, I’d think within +/- 5% is acceptable (technically that’s a measure of precision, not accuracy), but depending on what you’re dehumidifying, let us know.
I have several of the ZEN15 heavy duty smart plugs that aaiyar referred to and use them for sump pump, dehumidifier, radon fan, and washing machine. They have done the job well and appear to be built to handle that kind of load.
Be aware that any appliance with electronics will consume energy even when "off". And a device that doesn't such as a sump pump may occasionally register a non-zero value (e.g. 0.002). Also, the ZEN15 infrequently reports a value way off in the stratosphere like 20238 W. This is not frequent, though.
I agree that the Zooz ZEN15 is an awesome plug for appliances. I have a couple hooked up to window units, one connected to my washing machine, and one connected to a small space heater and haven't had any issues with them. For humidity, I'm not sure how accurate it is, but I am using a Zooz ZSE40 4-in-1 Sensor. I have used it in my painting booth out in the garage to make sure it isn't too humid or cold for painting. If needed, I have my space heater come on for a short period to warm up the area around the booth.
May I ask what driver you use with the KONKE
I've used two Zooz 4 in 1 sensors for humidity to control two dehumidifiers connected to Zooz Zen15 switches. I have them operating in a 2% range and they seem to be reasonably accurate and more importantly they are stable and consistent. They do track very closely to my two Ecobee thermostat humidity readings. You can set a temperature and humidity offset.
Update: 1/7/2020. These switches are not working well with the C-7. The join with SO security only and apparently can wreak havoc with the Z-wave mesh.
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Is there a good humidity and motion sensor that will work well with HE C7? I want to use it with a pair of Zooz switches to tun on the bathroom light and activate the fan when humidity gets high from the showers.
Since the original question was about an accurate humidity sensor, I will say that I was surprised by the Sonoff SNZB-02 (temperature + humidity sensor, zigbee). At first, I thought that it was garbage because it disagreed with every hygrometer in my house. Then I ran a "salt test" and it was actually the only accurate one! Temperature was not tightly controlled during the test, so I can only say that it was within a few percent.
One warning, though, is that it only updates humidity every 5 minutes. That is fine for my purposes, but if you are hoping for it to react to the first warm drop from your shower ... it will not.
thank you! i’ll check it out.
Those are out of stock until the end of May. Any thoughts on the Aeotec 6 in 1 - Battery Powered or the other one able to be powered over USB Aeotec 6 in 1 - USB/Battery Powered?
Occasionally you can still find them on ebay, but the Iris V3 motion sensors measure motion, humidity, and temperature quite well. And they are zigbee.
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FWIW a one point humidity reference is fairly easy to create:
A saturated mixture of salt (as pure as you can buy in the grocery store) and water, in a closed container with a small volume of air will result in ~72% RH.
I usually allow the mixture to stabilize for nearly a day, however I don't know the exact time needed to stabilize.
See the below for more detailed information.
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The folks that calibrate their cigar humidors have a ton of elaborate opinions on this. I just filled a bottle cap about half way with salt and enough water to just saturate up to the top surface of the salt. The cap and sensors go into a zip-lock back for at least a few hours.
As the table shows, you will simplify your life by finding a spot without much temperature fluctuation - away from windows, doors, HVAC vents, fireplace, etc. I found that the reading would swing a few extra percentage points if I did not heed this.
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I put my container in a cardboard box to slow down any changes.
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As many consumer humidity sensors are really only +/-5% accuracy anyway, I'm not sure it matters THAT much.
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I agree (I was going to say 100% but I wasn't sure that was precise).
However some of us have a personality disorder and because the salt solution is not the same hardware as the other 5 sensors I'm testing it is human nature to believe it above the hardware sensors. Then we can all put in our offsets and be happy campers. Fortunately the humidity drivers don't ask for a slope change or we'd all be in the nut house 
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In general, I agree. I went down this rabbit hole when a new sensor was reading >20% higher than old sensors. A simple scheme was needed to determine which (if any) were correct.
