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(Feb. 26, 2014) – You know the problem — you’ve burnt the toast and the smoke alarm won’t quit so you rip it from the wall or pull out the batteries. Consumer Reports tested a new combo smoke alarm and CO detector that offers a better solution. It’s from Nest Labs, the company that Google bought recently for more than three billion dollars.

The Nest combo smoke and carbon monoxide alarm promises to make safety more convenient. It warns you before the alarm sounds and you can shut off the alarm by waving in front of it.

Consumer Reports tested the $129 Nest first for carbon monoxide detection. The Nest came through. Next, the Nest was tested as a smoke detector. Testers lit some blocks of wood to create a smoky fire in a closed chamber. The Nest sounded quickly.

But Consumer Reports cautions that there are two different types of fire. There is the smoldering smoky kind of fire where there is no open flame and those are detected well by photoelectric sensors, the kind the Nest has. The other type of fire is a fast fire where there’s a flame and that’s detected best by an ionization detector, which the Nest does not have.

So when testers created a flaming fire, a Kidde alarm with both types of sensors sounded quickly. But the Nest did not. Based on its tests, Consumer Reports says you’re better off with a dual-sensor smoke alarm like the top-rated Kidde Pi9000 for $23.

Dual-sensor smoke alarms do not come in combination with a carbon monoxide detector. So you’ll need a separate CO detector. Consumer Reports says a good choice is the First Alert CO615 for $30.

Complete Ratings and recommendations on all kinds of products, including appliances, cars & trucks, and electronic gear, are available on Consumer Reports’ website. Subscribe to