Carbon monoxide has no smell, colour or taste, and it kills by stealth — often while people sleep. It's produced by any burning fuel: gas boilers, wood stoves, camping stoves used indoors, generators and paraffin heaters. In an emergency, when people improvise heating and cooking, the risk spikes. A CO alarm is the only reliable warning you'll get.
It's a small, inexpensive device that quite literally saves lives. Every home with a fuel-burning appliance should have one, and a portable unit is essential in caravans, boats, and anywhere you might run a stove or heater during a power cut.