Trying to keep 40 - 60% humidity inhouse during winter in Sweden can be tricky, the air often get too dry. I use this climate center to keep track of the humidity in the room and inside the three most important guitar cases. I simply put one transmitter in each case and the weather station will show the humidity inside the cases. After a while it gets apparent that different cases keep or absorb different amounts of humidity and it gets easy to compensate by using humidifier in the room and sometimes a humidor inside some of the cases.
This way I am sure to stay between 40% - 45% inside the cases all the time, and it saves a lot of adjustments on the guitars. Batteries have to be changed every two or three months, i use rechargeable batteries, very convenient.
Good tool!