Besides a good dose of common sense like getting a regular checkup on your gas appliances and not running your car in a closed garage there are a few simple devices that are a must have. Pictured here is a combination Smoke/ CO2 detector that is available in many stores and new homes are required to have them hardwired into the house electrical system with battery back up.
Speaking of batteries, many times due to being lazy (Or bad cooks) we unplug or remove a battery from a smoke detector and forget to put it back or worse negligently not put it back. I can think of no other device that will protect you all day and especially while you sleep.
Another tool that you should have and know how to use is a fire extinguisher, Consider yourself a first responder in this respect and if it is safe to do so you can employ a fire extinguisher. A classic example would be a cooking fire in your kitchen. A small box of baking soda can also come in handy to dowse a small grease fire in a pan as well as simply putting a lid on the offending pan. For larger more out of control fires your best coarse of action is to collect your loved ones and get out, forget your possessions they can always be replaced your life can not, evacuate and call 911 from outside of the home.
There are a few other options and combinations but water purification is a huge and specific subject worthy of it own blog so we will only touch the basics here in the article.