If you have a 200 to 300 capacity humidor (up to 8 cubic feet), and you don't want to be constantly checking and refilling your humidifier, then the Humi-Care EH Plus Electronic Humidifier is for you. Just fill the cartridge with distilled water and connect it to the fan unit, plug in the ribbon cable, set it in your humidor and you're done. The built-in humidistat will check the level in the humidor (factory preset at 70%, but it's adjustable), and if the humidity drops below the mark, the fan turns on, circulating moisture. When it reaches the target, it turns off. With the large capacity tank, you can go months between refills.
Spare cartridges for quick refills are available, and a fan kit which will help circulate the moisture better for larger humidors is an additional option.