UPDATE:  A mother, her boyfriend and two children are back home after their house filled with carbon monoxide Tuesday.

Police say it was all an accident caused by someone leaving a car running in the garage at the home on Brookplace Drive.

Guffey said it took hours for the home to air out.

"The levels were high in them. The levels inside the house were high. We had to ventilate the whole house. It took several hours to get all of it out of the whole house," he added.

Police say a car was accidentally left running in the garage causing the home to fill with the odorless and colorless gas.

Carbon monoxide poisons people who breathe it in and can cause death; that's why Guffey said it's important to have carbon monoxide detectors on every floor, outside every bedroom and in the basement of your home.

"You only need those if you're burning carbon-based fuel: natural gas, wood, propane. If you don't have any of those appliances in your house, then you don't really need one unless you have a garage where you're parking your cars," he said.

You can buy a carbon monoxide detector at your local hardware store for about $40. There are different kinds, and some detect smoke too.

"We have hardwired, which you're going to wire directly into your house's electrical system, battery powered, which is going to run on a regular 9-volt battery, and then there's ones that plug into a regular wall outlet," Samuel Bruns with Ace Hardware said.

It's important to remember to change the batteries twice a year. Every 3-5 years, you should replace the detector completely.

"If you don't remember when is the last time you replaced one, it's probably a good idea to go ahead and replace it," Bruns added.

To learn more about carbon monoxide, visit the CDC's website.

PREVIOUS STORY: Four people, including two children, are in the hospital after police said their home was filled with carbon monoxide.

It happened in a Soddy Daisy neighborhood just after 7:00 Tuesday morning.

Investigators said a man inside the home made the 911 call. They believe the carbon monoxide came from a vehicle that was left running inside the garage.

“We’ve seen them out,” neighbor Robert Lloyd said about the two kids. “Think about that little girl! That just kind of kills you.”

Lloyd lives five houses up the road from the home that was filled with carbon monoxide.

He said the family is quiet and their two toddlers play outside all the time.

“It tears your heart when you hear something like that with two toddlers down there,” said Lloyd, “you wonder how they survived.”

Police said the man inside the home called 911 to report the carbon monoxide.

Investigators were not able to tell us if anyone was in the car, or how long it was left on.

We also don’t know what alerted the family to the gas.

“I just can’t believe that’s intentional, that doesn’t make any sense. It has to be an accident,” urged Lloyd.

He said car engines can be extremely quiet and wonders if the family simply forgot. But his immediate concern was the two young children he hopes will be okay.

We don’t know if there are carbon monoxide detectors inside the home, but some neighbors said it’s an example of why every home should have them.

All four people are expected to be okay.

The case has been deemed an accident.

PREVIOUS STORY: A carbon monoxide investigation is underway in Soddy-Daisy.

The crime scene unit is currently at a home on Brookplace Drive.

Soddy-Daisy Police said officers responded to a 911 call about a home filled with carbon monoxide Tuesday. Two adults and two children were in the home.

The adult male made the 911 call, according to police. All four people were taken to the hospital to be checked out.

Police believe a vehicle that was left on in the garage could be the cause.

Channel 3 has a crew on scene. We will keep you updated as we learn more.