Why? Evaporation humidifier won't make more noise when they're empty, and water level detection is surprisingly hard to make reliable while still being convenie

Why? Evaporation humidifier won't make more noise when they're empty, and water level detection is surprisingly hard to make reliable while still being convenient in consumer devices. And you have to refill them daily anyway, so using it as an 'empty' indicator doesn't really add much (in theory it does, but not in real use). At best one could say it's the energy savings, but for a device that requires daily maintenance (refills) I'm not sure if the benefits outweight the advantages.