Off-duty Chicago police officer dies, woman critical after carbon monoxide leak in Albany Park home

“The police (said) he had been two plus hours late to pick up his son up so they did a check…(a neighbor) was working from home when she heard noise from a carbon monoxide detector that went off in one of the units of the home.”  This is concerning…why did the CO detector not alert them in time to evacuate safely?

https://abc7chicago.com/off-duty-cpd-officer-dies-woman-critical-after-carbon-monoxide-leak/6240387/?fbclid=IwAR3RfLF31PAK0eZzUOCrW0TRzxrW7crhRGm0xqvbCKrMAijyJw4Z0KFdppQ