> Sure, you can replace all your batteries really easily. But do you KNOW that the alarm is going to work? Sure. Push the button labeled "Test." (Cover your

> Sure, you can replace all your batteries really easily. But do you KNOW that the alarm is going to work? Sure. Push the button labeled "Test." (Cover your ears -- you should still be able to hear it.) Seeing the green glow on the Nest doesn't tell you that it'll wake you up when it goes off. So you have to test it anyway. Which makes it no better than a regular detector, from the assurance perspective.