I have a pretty humid apartment in Madrid and I'm thinking about getting a smart humidity sensor to monitor it from my phone. I've seen several on Amazon but I'm not sure if they actually measure humidity properly or if it's just marketing. Does anyone use them and how do they work in practice?
Most cheap humidity sensors from Amazon have a margin of error of a few percentage points, so they work fine for figuring out if your apartment is too humid, but don't expect lab-grade accuracy. What is useful is being able to monitor trends from your phone and act before mold forms, especially in Madrid where relative humidity can be pretty stable. The real problem is that some models lose calibration over time, so if you get one, pick a well-known brand with good reviews and keep your receipt just in case.
Seconding what they say about the margin of error - those cheap sensors work to give you a general idea, but what most people don't mention is that many lose accuracy if you put them in places with air currents or exposed directly to sunlight, so where you install them matters just as much as which sensor you buy. For Madrid with that humidity problem, they're useful for knowing whether you need a dehumidifier or to open windows, but if you want exact monitoring for something medical or technical, better to invest in a more serious one or straight-up go for an analog wall hygrometer, which is more reliable.
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