CHICAGO (CBS) – A Chicago family avoided tragedy when a 911 call for one family member ended up saving the entire family from a silent killer.

Emergency responders initially got a call for a person down inside the home near North Sawyer Avenue and West Ohio Street. Once inside the home, their alarms for carbon monoxide detection went off.

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“We wear this all the time on our radio strap, and it’s always turned on, kept in the case, and it will start to beep,” said Anne Gradolf, ambulance commander for the Chicago Fire Department.

“It will alert them to an elevated level of carbon monoxide, which in turn as this morning, it allows them to notify other aspects of the fire department,” said Rich Savoia, Engine 16 Fire Lieutenant with the Chicago Fire Department.

Paramedics say the device goes off when it detects more than 10 parts per million. Some parts of the house had a read of 800 parts per million.

Anne Gradolf, ambulance commander for the Chicago Fire Department, explains operation of carbon monoxide detectors.

Firefighters say they believe this could have been a deadly outcome for the family. Nine people were taken to the hospital, and, had someone not called 911 sooner rather than later, it could have been too late.

The situation prompted a call for extra ambulances on scene. Eight adults and one child were taken to the hospital in stable condition.

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“Unfortunately over the years in the City of Chicago we’ve had some instances where we’ve had more than one person succumb to that situation,” Savoia said.

“We’ve ended up evacuating the homes. People have said ‘Oh my good, I thought I just had the flu,’” said Gradolf.

Savoia and Gradolf did not respond to this call but has been on similar calls in the past.

“It attaches to your blood cells and it blocks the ability of your blood to accept oxygen. So you kinda, over a period of time, you fall asleep and you don’t wake up,” he said.

Carbon monoxide is described as an odorless and colorless gas. The symptoms of carbon monoxide poisoning are very similar to having the flu. The symptoms include dizziness, headaches, extreme fatigue, upset stomach and vomiting.

“It’s extremely important that everybody has not only a smoke detector, obviously, in their home but a carbon monoxide protector,” Savoia said.

“It’s not just a winter time issue. There can be times that this can go off at any time of year – your hot water heater, something else can be activating it – so people should be alert all year long,” Gradolf said.

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All nine family members are now recovering at Presence Saints Mary and Elizabeth Medical Center.