CCengineer

The CO sensor in Nest is designed to last 7 years. The Nest has a built in timer that will start chirping after 7 years, forcing you to throw it away.

Most modern CO alarms last 10 years. Nest chose the smaller sensor, which dies sooner. Very poor decision on their part.

For more detail: Nest uses a CO sensor by Figaro, TGS5342. This is a smaller version of Figaro's TGS5042. The CO sensor is filled with a water reservoir, with some air inlets to let gas enter. Over several years, the water evaporates out of those air inlets and the sensor dies.

Nest's smaller sensor has as smaller water reservoir, which means it doesn't last as long as the other alarms with a larger reservoir. First Alert uses the larger TGS5042 sensor, therefore it lasts longer. Kidde uses their own sensor, which also lasts 10 years.

Like I said in another thread, I'm an engineer for a smoke alarm company; so my advice may be biased....

There are smoke alarm alternatives available, but they're very expensive. Nest is a high priced gadget / toy that must be thrown out after 7 years. You're better off buying a First Alert or Kidde photoelectric smoke alarm with a 10 year battery. Then you'll never have to worry about it for 10 years. They'll cost around $30-$40 each.

If you want a higher-end serious fire protection system, there are alternatives if you look around. Crossfire alarms are very good (although their website may not be...) They are made in USA (even the plastic injection molding, circuit board assembly, etc).

They are wirelessly interconnected, photoelectric smoke alarms with a 10-year battery. They have a heat alarm for the garage, kitchen, furnace closet, attic, etc. These are places you can't put a smoke alarm, but also places where fires actually begin. You have smoke alarms in your bedrooms, hallway, and living room; but fires rarely start there. They also have a carbon monoxide alarm; and all the alarms set each other off. If there's a fire in your garage, the alarm in your bedroom goes off.

They're also coming out with products that will send you a text message and call the fire department, and products for the elderly, children, and hearing impaired.

These are very high-end systems, and are very expensive (even more than Nest). They're sold only by dealers who professionally evaluate the home and install them. This also adds to their cost - you're buying an alarm plus a salesman plus an installer.

Companies like ADT and AT&T offer good systems that can call the fire department and have other features. But, they're expensive, have a monthly fee, and are usually based on normal cheapo alarms.

There's a few options; but none of them are perfect...

First, I'll preface this that I'm an engineer for a smoke alarm company, so I may be a bit biased. The simple answer is that the rules forbid a smoke alarm feature like you (and many others) would like. Fortunately, if you switch to a photoelectric alarm in a proper location, you should not get false alarms from cooking.

Now here's the long answer: Essentially all smoke alarms in the United States are tested and listed to UL217, which has specific requirements and restrictions for smoke alarms. UL217, Section 7 discusses alarm silencing means. Among many other things, it says

"It is not prohibited that each single and multiple station smoke alarm be provided with an automatically resettable alarm silencing means that has a fixed or variable time setting which desensitizes the alarm for a maximum of 15 minutes. Alarm silencing shall not disable the smoke alarm. Sensitivity shall not be reduced to more than 4 percent per foot of obscuration."

So we're only allowed to slightly desensitize the alarm for up to 15 minutes; never disable it.

Fortunately, the whole problem is moot if you switch to a photoelectric alarm (around $25) instead of an ionization alarm (<$10). Ionization alarms will false alarm from cooking byproducts far too quickly; photoelectric alarm generally do not. You also should not place a smoke alarm in the kitchen (this is a perfect location for heat alarms).

While ionization alarms will go off far too quickly from cooking, they also fail to response to slow smoldering fires. There are many videos of rooms and test boxes filled with smoke that fail to trigger an ionization alarm, while the photoelectric alarm is working fine. Some states have even outlawed ionization alarms.

Buy a decent photoelectric alarm with a 10-year battery, like the ones made by First Alert or Kidde, and you probably won't have to worry about your smoke alarms for 10 years. That's even better than Nest that needs to be thrown away after 7 years.

I don't work for any of the companies mentioned above either...