Most consumer-grade hygrometers, including brands like Unni, ThermoPro, Govee, and Veanic, are not reliable enough for monitoring the humidity around a valuable instrument like a piano. These devices often claim ±5% RH accuracy, but real-world testing frequently shows fluctuations of 10% or more. This means your hygrometer might be telling you it’s 40% humidity, when it’s actually barely 30%!
In the cover photo for this article, you can see an Unni hygrometer reading 34% next to a more accurate Reed device reading 25.4%. If you looked at the Unni, you might think the humidity was a bit low. However, according to the Reed, the situation is much worse! And inexpensive hygrometers only get less accurate the more extreme the humidity gets, which makes it even harder to get an accurate idea.
Using an inexpensive hygrometer can create a false sense of security. They wrongly reassure you that your instrument is safe when, in reality, conditions are much worse. Low humidity risks soundboard cracks, while high humidity risks swelling, mold sticking keys.
Many of these hygrometers lack proper factory calibration and cannot be recalibrated, meaning any inaccuracies out of the box or sensor drift over time cannot be corrected. Additionally, their sensors tend to be slow to respond to environmental changes and may suffer from hysteresis, where they fail to return to accurate readings after large humidity fluctuations. This means that even if they read correctly one day, they may be significantly off the next.
Beyond accuracy issues, these low-cost hygrometers are frequently poorly constructed, with cheap plastic casings, low-quality sensors, and short lifespans. Many models degrade over time, leading to even greater inaccuracy! Their batteries may drain quickly due to inefficient power design.
Oasis OH-2 Hygrometer
I recommend these to customers regularly. They’re still fairly inexpensive (about $30), but are considerably more accurate than the majority of consumer hygrometers. You can purchase them from Amazon or from Sweetwater.
Temp Stick Remote Wi-Fi Sensor
The Temp Stick Wi-Fi Temperature & Humidity Sensor offers 24/7 remote monitoring, real-time text alerts, and detailed data logging. Whether you’re on vacation, the piano is in a seasonal home, or you’re just wondering what’s happening when you’re away, the Temp Stick is monitoring! It instantly notifies you if humidity drops too low or spikes too high, helping you act before damage occurs. It’s more accurate and precise than most consumer hygrometers.
The Oasis hygrometers above are good, but if you’d like to take your monitoring to the next level, or if your piano is unattended for long periods, these are worth considering! You can purchase the Temp Stick from Amazon. These are approximately $150.
Testo 602-H1 Hygrometer
This is definitely the most expensive option, but it’s extremely accurate. They also have the 602-H2, which includes a visible flashing alarm when the humidity is outside the desired range. You can order the Testo 602-H1 Hygrometer directly from Testo. This much accuracy isn’t useful if you’re in an environment with large humidity swings — I don’t recommend it to most customers. However, if you have a very high-value instrument in a well-controlled environment, this tool gives you the highest accuracy. It makes sure you’re giving your piano the very best! However, this does not do any remote monitoring. These are approximately $130.
