Ortega HUMIBUSTER100 with 100mm Diameter for Most Acoustic Guitars and B

Ortega Guitars Soundhole Humidifier and Feedback Killer in One for Acoustic Guitars (HUMIBUSTER100)

D'Addario Accessories Guitar Humidifier System - Humidipak Maintain Kit - Automatic Humidity Control System - Maintenance-Free, Two-Way Humidity Control System For Guitars

MusicNomad (MN311) The Humitar ONE-Acoustic Guitar Humidifier & Hygrometer