No batteries are necessary to keep an eye on your relative case humidity!
These fast reacting humidifiers can be added to any case where there is room. Either use the included double-sided tape foam ring to stick into the case where it won’t come loose and damage your instrument, store in an interior compartment, or insert the back into a 1 3/8 inch diameter by 1/4 inch deep hole on the case interior (can be cut from some foam cases). These hygrometers are very fast-acting to changes in humidity as they allow the free flow of air to a hydro-reactive coil through large gaps behind the gold outer ring. However, while they are calibrated and can be re-calibrated using a screwdriver on the back of the device, they should only be used as a relative indicator, rather than for precise measurement. We recommend calibrating to an electric hygrometer at 50% humidity, then adding moisture to the case by humidifier if the device reads below the marked “Normal” range.
This device is not a humidifier and does not add or remove moisture from your case.