Most people die from smoke inhalation while they are sleeping, not from actual flames. Smoke alarms cut the risk of dying if a home fire occurs by 50%. Batteries should be replaced at lease once a year and tested monthly. The fire marshal's office recommends that you change the batteries each time that you change your clocks.
When using a space heater, you should:
Not use a space heater with an extension cord
Not use a space heater with missing or broken parts
Only use space heaters equipped with tip-over switches
Place space heaters away from combustible materials