Carbon monoxide is referred to as the silent killer. It’s odorless, invisible, and strikes when you least expect it. It’s also more likely to hit during winter than at any other time.

With that in mind, a number of states are now requiring carbon monoxide detectors in homes. Kentucky, Washington and Oregon made moves this year to require CO2 detectors in all new properties. This coming January, Arkansas will join them. California and Wisconsin also mandate that all existing single-family homes have them fitted.

“We’re seeing more states address this issue,” partly because of well-publicized deaths from CO poisoning, says Scott Hendrick of the National Conference of State Legislatures.

Any home that burns fossil fuels is susceptible to carbon monoxide. The gas is a byproduct of the combustion of that fossil fuel and any leak in the system can allow CO2 to escape into the home. A buildup of CO2 can lead to headaches, illness or even death in extreme circumstances.

A simple CO2 detector analyzes the air and alerts homeowners or corporate housing tenants when the levels of CO2 rise above a given threshold. Simply opening windows and turning off the furnace will allow gas levels to reduce while you have the system inspected.

Carbon monoxide can enter a home without anyone seeing or smelling anything. Fuel-burning appliances, such as gas stoves, furnaces, fireplaces and generators, or cars left running in an attached garage all risk CO2 entering the home. Exposure symptoms include headache, fatigue, nausea and dizziness.

According to the Centers for Disease Control and Prevention, there are 500 deaths and over 15,000 hospital admissions as a direct result of CO2 poisoning each year.

“We see a large number of deaths after storms and power outages, because people bring generators into their homes or garages,” says Patty Davis of the U.S. Consumer Product Safety Commission. She says generators need to remain far away from the house.

Surprisingly, there are some of don’t see carbon monoxide detectors as necessary. Larry Brown, director of codes and standards for the National Association of Home Builders says, “it doesn’t make sense” to require them in all homes. The NAHB helped defeat a building-code effort last year to extend the CO device requirement to existing properties.

Whatever your personal opinion, a $20 CO2 alarm that only needs replacing every 5 years isn’t a lot of money to spend on your family’s safety. Any home that uses fossil fuels is at risk of a CO2 leak, which is why regular servicing and a CO2 detector is a good idea.

The increased number of states requiring CO2 detectors in new homes is increasing, which can only be a good thing. Given the money involved, and the fact many building firms will pay nothing like the $20 for a proper alarm, the argument against them lacks strength. Even if we reduce the number of deaths by a few, it makes it all worthwhile.