I had a natural gas detector and a carbon monoxide detector at my old house. I came home from work one day to the gas alarming like crazy and flashing red. I called the gas company, they told me to get out of the house immediately and not to touch any light switches or take anything. Just get out now, they said. They came and they brought the fire department. A gas line had broken under my home, they evacuated my whole street for the night while they dug up my basement and my street to repair it. My neighbors all blamed me for the inconvenience (as if I broke the gas line under the house? wth?!) but lucky we had the gas detector cuz I did not smell the gas that bad, just a little bit and the whole street could have blown up. The gas company said the levels in my home were an emergency.