If you love your guitar (or other wooden instrument) then you need to listen up. Controlling the humidity in the air surrounding your guitar is very crucial. You do not want your guitar to get too dry or wet. Either one is bad. You need to take advantage of technology that is available to protect your investment.
I use the Boveda for Music Humidifier. It takes all the hassle, mess and mystery out of maintaining your guitar. Boveda is smart enough to monitor ambient conditions and will add or remove moisture to maintain 40-55% RH (relative humidity) in your guitar case. And because it requires no activation or maintenance, you spend more time playing your perfectly-maintained guitar.
I lost a vintage Fender Precision bass to these kinds of problems, so never again for me. I keep my instruments in their cases and use the Boveda humidifier to keep things safe and sane. I switch the packs (they sell refills) every three months. It's a small price to pay for peace of mind.
The 49% RH Boveda are designed to keep a specific range of humidity instead of a specific relative humidity as they are designed specifically to humidify wooden instruments, which should be kept between 40-60% relative humidity. To maximize the lifespan of the 49% Boveda packs, they start at the top of the range – high 50’s – and as they release their moisture end at the bottom of the range – low 40’s.
They work on a principle that certain salts mixed with water will naturally regulate humidity. Boveda absorbs and emits only purified water vapor through its semipermeable membrane and does not damage material through direct contact.
I keep a reminder in my calendar that it's time to replace the packets but you can tell when they need to be replaced because they get hard (solidify).
To see the latest price on Amazon, visit the Boveda Page Link