Product review (5 stars): An easy solution to dry climates and acoustic guitars
Easy to use. the hygrometer/thermometer is quite sensitive - adjusts to humidity and temperature quickly. The humidifying sponge holds a good amount of water with no drip. The best part about the humidifier is that it doesn't hurt the strings, but can be left in while moving the guitar in it's case. I had never used something like this in my acoustic guitars, but a friend recommended that I get something. When it gets real cold in the winter, the house humidifier (aprilaire on the furnace) can't keep up. I leave the hygrometer/thermometer out in the room where my guitars are. If I want to check the guitar, I take out the humidifier and put the hygrometer in the guitar and close the case. Come back about 5 minutes later and it gives an accurate reading of the interior of the guitar.  The only supplies I see I'll need to purchase is distilled water. If I used tap water, I'd have to replace the synthetic sponges frequently. The directions recommend this & grocery stores carry distilled water in gallon jugs.