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Your Nest Protect questions. Our answers.

An exploded view of Nest Protect

Since the introduction of Nest Protect, it seems like everyone’s talking about smoke and carbon monoxide (CO) alarms. While we were developing Nest Protect, we were only able to talk to industry experts, friends and family. So, we’re excited to finally talk to you and answer some of the questions we’ve been hearing. Fire and CO safety are complex topics and can be confusing. I thought this would be a good way to clear a few things up.

These answers are based on information that’s specific to the US. We’ll be adding UK and Canada information soon.

“I’ve heard carbon monoxide is heavier than air. Shouldn’t a carbon monoxide alarm be near the floor?”

It’s a common misconception that CO alarms have to be installed close to the floor. This is because some CO alarms need to be plugged in and typically outlets are near the floor. According to the National Fire Protection Association, the height of a CO alarm doesn’t affect detection. CO is actually lighter than air and will mix evenly. This means a CO alarm can do its job wherever it is in the room.

Learn more about CO >

Because Nest Protect is a smoke and CO alarm, it’s required by law that it be on the ceiling or high on a wall. Smoke definitely rises.

Where to install Nest Protect >

“Is it okay to install a smoke and CO alarm in the attic? Or basement, kitchen, or garage?”

These areas are a little different than the bedrooms, hallways and common areas of your home. Each of these areas has its own unique rules for installing alarms because of temperature changes, cooking appliances, or other factors.

  • Attic: It’s true that unfinished attics are a bad place for smoke alarms. The National Fire Protection Association (NFPA) prohibits installing an alarm in an unfinished attic because the temperature can drop below 40ºF (4ºC) or get above 100ºF (37ºC) and the smoke alarm may not function properly. A finished attic, like a game room, is a different story. Here, you can install a Nest Protect.

  • Basement: It’s a myth that you shouldn’t install an alarm in the basement. The NFPA actually recommends installing a smoke and CO alarm because common sources of fire and CO leaks such as your furnace or hot water heater are often located in the basement. If all you have is an unheated crawl space, that’s not the right place for a smoke alarm.

  • Kitchen: Kitchens are not the best place for smoke alarms. Smoke alarms should be at least 10 feet (3 meters) from cooking appliances; and some building codes require 20 feet. This helps to cut down on false alarms. So if you have a smaller kitchen, it’s better to install Nest Protect in the hallway nearby.

  • Garage: Because of heat fluctuations and car exhaust, it’s not a good idea to have a smoke and CO alarm in your garage. The NFPA actually prohibits it.

This information is based on NFPA recommendations on placement (NFPA 72 for Smoke Alarms and NFPA 720 for CO Alarms). Always refer to your local codes before beginning any installation.

Which rooms need a Nest Protect? >

“Can I buy a Nest Protect and connect it to my existing smoke and carbon monoxide alarms?”

Unfortunately no, but this isn’t unusual. Each company’s smoke and CO alarms use proprietary detection algorithms and interfaces. And therefore there’s no industry standard. If alarms from different companies are connected together, they may not warn you properly in an emergency. The NFPA actually prohibits the connection of alarms from different manufacturers without special testing. To the best of our knowledge, no company sells a combination smoke and CO alarm that is meant to be connected with a different company’s smoke and CO alarm. Some companies even state in their documentation not to connect to a different company’s smoke and CO alarm.

“Why doesn’t Nest Protect use wired interconnect?”

Interconnect is the way that the Nest Protect in the hallway tells all of your other Nest Protects when there’s a problem. Both Nest Protect (Wired 120V) and Nest Protect (Battery) have interconnect.

We looked at many different ways to connect Nest Protects together and consulted with fire safety experts such as the NFPA along the way. In the end, wireless interconnect was the best option. You can add more alarms without adding expensive wiring. And wireless interconnect allows Nest Protect to convey more safety information in an emergency.

When the Nest Protect in the hallway says, “Emergency, there’s smoke in the hallway,” your other Nest Protects will say the same thing. With traditional hard-wired alarms, the other devices can’t tell you where the problem is.

Learn more about wireless interconnect >

Wireless Interconnect Wired Interconnect
Can convey the type of danger throughout the home
Can convey where the danger is throughout the home
Can add and connect new alarms without rewiring
Place alarms on any wall or ceiling without wire constraints



To interconnect, Nest Protect uses its own wireless network, not your home’s Wi-Fi network. So, even if your Wi-Fi goes down, your Nest Protects will still talk to each other.

Fire safety experts such as UL and the California State Fire Marshal have thoroughly reviewed and tested our wireless interconnect and confirmed it meets national safety standards.

How was Nest Protect certified? >

“Can I replace my wired interconnect alarms with wireless interconnect alarms?”

The NFPA doesn’t have a preference for either wired or wireless interconnect. Additionally, the International Residential Code considers smoke and CO alarms with either wired and wireless interconnect to be equal under its most recent model building code. To the best of our knowledge, there are no state building codes that require hard-wire interconnect for your smoke and CO alarms. However, you should always check your local fire safety codes. They can vary from city to city or even home to home.

Wireless Interconnect Wired Interconnect
Permitted by National Fire Protection Association (NFPA)
Permitted by International Residential Code
Permitted by all states



“Why do I need the Nest app to set up Nest Protect?”

You can install a Nest Protect without the Nest app. It will function as a standalone smoke and CO alarm and sound the alert if it senses a problem. If you have more than one Nest Protect, you need the app to connect them together and get all the features. After everything’s set up, the app lets you check the sensors and batteries whenever you’d like and get a message on your smartphone if something goes wrong at home.

“Why do I have to replace Nest Protect after seven years?”

Just like any electrical appliance, smoke and CO alarms wear out over time and must be replaced before they’re unable to warn you in the event of an emergency. National standards and state laws require alarms be replaced when the sensors expire and most CO alarms have a lifespan of five to seven years.

Nest Protect has been fully tested by UL (U.S. and Canada) and BSI (Europe) and has an expected lifetime of seven years, based on the life of the CO sensor. To ensure your safety, Nest Protect checks its sensors constantly and sends you an alert when your alarm needs to be replaced. Even if an alarm doesn’t have a CO sensor, laws require that smoke alarms be replaced every ten years.

Learn more about replacing Nest Protect >

Why can I only add 10 Nest Protects to my account? (Yes, this came up more than once.)

Wow, we love the enthusiasm. We’ve heard you and we’re working on adding more. Stay tuned.


If you have other questions, please add them to the comments below. We may do this again. And thank you for all the questions you’ve already asked. We love talking about Nest Protect.