The 2nd generation Nest Protect has been redesigned from the inside out. It has a split-spectrum sensor, tests itself automatically and lasts up to a decade. It’s also the first home alarm you can hush from your phone without any extra hardware required. And it tells you vocally what’s wrong and where the danger is. It also sends alerts immediately to your smartphone.13.5 x 13.5 x 3.85 in. White.