Install smoke alarms; add CO alarms if you burn fuel indoors
Working alarms beat your nose while you sleep. If you burn fuel indoors (furnace, fireplace, generator, gas stove), you need carbon monoxide detection as well.
What the evidence says
A 1998 JAMA study (Marshall et al.) found that a working smoke alarm was associated with an odds ratio of about 0.39 for death in fatal residential fires (95% CI 0.18 to 0.83). The CDC reports hundreds of US deaths per year from unintentional non-fire carbon monoxide poisoning.
Evidence grade: B: observational studies plus surveillance, with strong public-health consensus. See how we grade evidence.
What to do
Put alarms on every level and outside sleeping areas. Test them monthly. Never heat a home with an oven or grill.
Where rules differ
Rental requirements vary (US states, England regulations). Check your local rules.