The Nest Protect is a highly evolved makeover of a dinosaur of an appliance, the humble smoke and carbon monoxide detector. It’s self-aware: if the “emergency” is just a little burning toast, you can silence the alarm simply by waving at it. It’s also sleekly designed and networked: all the Nest Protect units in your house talk to one another and to your smartphone, so they can text you when their batteries are running low.