Guitarists have been using "sound hole" humidifiers since the 1960's. These humidifiers have significant shortcomings. You cant see when they need to be refilled, and when you do refill them, they can be overfilled and drip inside your expensive instrument. This is because all currently available "sound hole" humidifiers have openings to allow for water evaporation. The job of protecting your guitar against leaks is left to an absorbent medium like a sponge or floral foam, which can be easily over saturated with water. • MFSKU OH-1 • UPC 898775001007