In a home fire, the risk of dying is cut in half if you have a working smoke alarm. But National Fire Protection Association statistics found that alarms only sounded in half of the home fires reported to fire departments between 2007 and 2011.

There are basically two types of fires: smoky, smoldering fires that are best detected by alarms with photoelectric sensors and fast fires with flames that are best detected by alarms with ionization sensors.

Consumer Reports says you’re safest with an alarm that quickly detects both types of fire, such as the dual-sensor models it recommends: the Kidde PI2010 and the First Alert 3120B. They cost around $40.

Consumer Reports also tested an updated version of the Nest Protect. It’s a $99 combination smoke and carbon monoxide alarm. Tests found that the new Nest is still slower to respond than other smoke alarms to flash-flame fires.

The Nest is equipped only with a photoelectric smoke detector. For optimal safety, Consumer Reports says that it’s best to skip the Nest and buy a dual-sensor smoke alarm and a separate carbon monoxide alarm.

Consumer Reports recommends the First Alert CO615 carbon monoxide alarm for $50.

Only about one-third of homes have a carbon monoxide detector. But Consumer Reports says a CO detector is a must in any household with fuel-burning appliances such as a furnace, water heater, range, cooktop, or grill. Even an all-electric home can benefit from a couple of CO alarms if you own and use a generator.