I can only really hear it when i have everything off in my apartment. It clicks, but if you have the tv on, or even a space heater you won't be able to hear it. It works fine for my two snakes, and the are well worth the money. What clicks louder for me is the cheap timer I have for the lamp on my big tank. I set it to stay on for an hour and a half, and it goes off for a half hour and when the light goes off or comes back on, it clicks really loud.