The Waterloo Fire Department is crediting a working carbon monoxide (CO) detector for potentially helping to save the lives of two people early Sunday morning.

Around 3 a.m., firefighters and paramedics responded to an apartment on Princess Street where they rescued two people from inside of a unit.

Officials said they were exhibiting signs of carbon monoxide poisoning and “not responding well.”

“If they didn’t have a detector, things could have been catastrophic,” an official told CTV News.

Waterloo fire said Enbridge gas will be coming and investigating, as it is suspected the leak came from a gas-fired appliance.

The fire department is reminding people that CO detectors are mandatory and good for seven years.