Extech RHM15 - Mini Hygro‑Thermometer Monitor – Pocket‑Sized Humidity & Temperature Meter (°F), Min/Max Memory, Built‑in Stand

If you like to know what your guitar case humidity is, this is an ideal little device. I have one in each of the cases, and use in conjunction with the D'Addario Humidi-pak units.

Excellent Very accurate

Some customers may look at a few thermometer and just buy a couple, without looking or reading too much. But note that this one is really small and it needs a Mercury battery to power it. So it is fine if you use it for 1 or 2 years, but what about after that? Will you spend money buying expensive Mercury batterie's again? My usual action is just to use the ones that can use a rechargeable AAA battery, so this small one will probably sit in the drawer. Just something to consider before you buy.

I bought this unit based on 2 things. 1st this company Extech has been around since 1971 and my other choice was the inkbird who have less than 10 & 2nd Taylor guitars offers these on the site, even though I don't own a Taylor. Also the Inkbird and Oasis specs state the low end of the RH is 30% , in their reviews people state at that point they show no reading, where the Extech RMF15 reads down to 10% which for me is more helpful. It worked as soon as I removed the battery which is the only way to remove the thin plastic cover that prevents the unit from powering on since it's under the battery , I didn't have any trouble removing the battery cover . I only have one other hygrometer which is a Stewmac analog that is about 4 1/2" in diameter and it always seemed to be accurate based on a few decades of living where I do and how everything wood here changes when it's quite dry . I admit I was concerned this Extech model RHM15 would be far off from the 4 year old analog Stewmac yet after 4 hours they both read one degree difference it temp as well as RH . I keep my few guitars in a small closet and in their hard shell cases and placed the Extech right next to the Stewmac . I bought this mainly to have a unit I can place in the guitars case and have a min/max reading . Since it reads so close to the large analog unit which does read in temp and RH very close to what the hour to hour weather report states as well as how one can tell if it's to dry or damp based on their hair and skin and wood in the home. I feel confident it reads as close as I'm going to get and will offer me very close temp and RH in the guitars case. Sure one can spend a lot more by buying a professional unit . From what I used as reference above it's reads very close to right on and am glad I made this choice.

Don’t waste your money on this item. It is not accurate. Temperature is over 10 degrees off and humidity is of by at least 20%.

Purchased 2nd one to check guitar cases. 1st one worked well and helped me check humidity. Its winter so air is a bit dryer guitars are pulling all the moisture out of those humidipacs. Good to know though.

It's okay. Kind of small.

I have had this meter for three months without issues. I have yet to replace the battery. the temperature reads the same as my digital wall clock with a thermometer. The humidity varies throughout the day so I know it is reading the air, but I have nothing to compare the reading to, so I only assume it is fairly accurate.