This Oasis hygrometer, ($24.95) works great! I attached mine to the hatch of the storage compartment in my guitar case. I keep it set off to one side so the neck of the guitar clears it. The Oasis hygrometer, ($24.95) main draw back is that it stays on. You need to turn it off to save the battery. The Oasis hygrometer, ($24.95) gives you instant measurements of temperature and humidity. A guitar, or any other stringed musical instrument made of wood, is at risk of cracking when the relative humidity drops below 40%. The Oasis® Digital Hygrometer ($24.95), accurately measures relative humidity and can help you decide when to use your Oasis® Guitar Humidifier. With our new convenient case clip, it is now possible to measure the relative humidity inside your guitar case with the Oasis® Digital Hydrometer ($24.95). This unit works great for helping to humidify violin family, humidify mandolins, humidify dulcimers, humidify mandolins and any other wooden, stringed instrument. Oasis® Digital Hygrometer/Thermometer ($24.95) (3.0 v 2032 battery included - annual replacement needed) * Guaranteed for 5 full years * Super-slim profile design with secure Velcro mount fits anywhere * Advanced humidity sensor maintains exceptional accuracy for years * Records high/low temperatures * Measures temperature in C or F * On/off switch Oasis Digital Hygrometer/Thermometer OH-2$24.95 Oasis Guitar Humidifier $16.99 Oasis OH11 clip on tuner Regular price: $16.95 Sale price: $14.95