This mini analog 2 in 1 thermometer and hygrometer won't break the bank and will help you look after your plants at the same time (win win). Yes, they are cheap, but this mini temperature and humidity gauge works a treat. Can you tell I had low expectations at this price? Pretty happy to be proven wrong. Plus considering it's plastic, not metal, and doesn't need batteries I'm actually quietly impressed. 

I mean, I wouldn't be relying on this to make life or death plant decisions, not at all, but if you want something you can pop in your grow house or plant tank, or pop in amongst your plants, to keep an eye on highs and lows, without the risk of mixing batteries and water, this analog, mechanical meter is your guy. 

Thermometer and Hygrometer

You'll see there are two dials. The larger dial tells you the temperature, from minus 30 up to 50 degrees celsius. The smaller dial keeps track of humidity, from 10% to 100% humidity all with no battery required. 

I've been running a few tests around the house, and it's accurate to about 1 to 2 degrees (when there are temperature and humidity fluctuations analog meters display the average). It takes a few minutes to react to a change in temperature or humidity when you move it to a new spot (these don't display a change as fast as a digital meter does). 

Not as accurate as fast as a digital thermometer sure, but no batteries to replace? Nothing to have to plug in? I'm happy. You can also calibrate both gauges if needed using the screws on the back.  

Mini size - 5.5cms

At just 5.5cms wide and 1.5cm thick, this chap's small enough to be placed anywhere, and being plastic, also light enough to hang off a pin or picture hook. There's a little cut-out in the back that makes it easy to hang (check out the photos). The other two cut-outs you see in the photo of the back of it give you access to the two screws for calibration.

I just sit mine in amongst my plants facing up so it's easy to read at a glance. I move it to my different plant shelves to keep an eye on general conditions. In winter I've been using mine to check my heaters are reaching to and keeping the areas my plant shelves are in above 15 degrees, and to know when to run my H2O Humidifer to keep that humidity up.  

How does an analog hygrometer work without batteries?

Analog hygrometers measure changes in moisture using a metal strip attached to hydroscopic material (usually a type of paper that has plastic in it but still absorbs water). As the polymer absorbs water the polymer expands but the metal strip doesn’t, causing a coil to rotate, moving the needle on the dial. In dry conditions moisture evaporates and the coil contracts, moving the dial the other way.

How does an analog thermometer work without batteries?

Analog thermometers work in a similar way but using a temperature-sensitive coil of metal called a bimetallic strip, which expands as it gets warmer and contracts as it cools, moving the dial up or down as the temperature changes.