Allentown firefighters are calling it a close call.
A carbon monoxide detector went off in a row house on Turner Street, and it was actually picking up gas levels from the house next door, officials said.
Six homes had to be evacuated. Three of them had carbon monoxide readings at lethal levels, officials said.
"I went shopping. I was gone three hours. I come back, the carbon monoxide thing was going off in the basement," said Carolyn Loper, who lives in the home where the detector went off.
Loper said she called 911 and was told to leave the house immediately.
When firefighters arrived, they picked up readings of 900 parts per million in the house where the problem began.
“At those levels, you're going to be dizzy and nauseous in a couple of hours. Next thing, you're going to be unconscious. At that point, we're talking about lethal levels,” said Capt. John Christopher, Allentown Fire Dept.
The problem, Christopher said, was caused by a bird's nest that got stuck in the flue of the chimney.
Neighbor Cynthia Brown said she's thankful the problem was caught at the right time.
“The gentleman that lives on the second floor asked for the heat to be put on today because we're supposed to get a cold front tonight. If he wouldn't have said something and her thing wouldn't have went off, the fire department said we would've all been dead,” she said.
"If this sort of thing happened at 11 and 11:30 at night and you don't have a detector, there's no way of knowing. You might not wake up," added Christopher.
Unlike smoke detectors, CO detectors aren't required in homes, but Christopher said every home should have one and it should be placed in a room where the alarm would wake you up if it went off.