As of July 1, California law requires all homes to have a carbon monoxide detectors.
Does this mean that if you don't install detectors you may have a visit from your local police or fire department? Probably not.
No one is expecting a California civil servant to knock on your door to inspect for a proper installation. Instead, they have passed along this responsibility to your local real estate agent. He or she will make sure that alarms are installed prior to the purchase or sale of a home.
Before we dig into the law let's talk about carbon monoxide vs. carbon dioxide.
Carbon monoxide has been called the invisible killer because it is a colorless, odorless, tasteless, toxic gas. According to the Centers for Disease Control, 15,000 people per year are treated for carbon monoxide poisoning in the U.S., and approximately 500 of these poisonings result in death.
Carbon monoxide is a gas that is created when fossil fuel (example: natural gas) is partially burned. When fossil fuels are fully burned they create carbon dioxide and steam, both of which are safe to breathe.
When we inhale carbon monoxide our bodies are fooled into thinking that it's oxygen so our natural alert system, the gasp for air, is short-circuited. The lack of oxygen makes us drowsy and can lead to a very unfortunate outcome.
One of the reasons the carbon monoxide poisoning is on the rise is that new homes are built to such high energy standards that they don't "breathe." That is to say, there is very little air transfer between the interior and exterior so bad gases are trapped indoors.
When purchasing a detector consider buying the combination alarm (smoke and carbon monoxide). They are not much more expensive, you'll have one less device to clutter your ceiling and you may save yourself the eventual inconvenience of trying to determine which alarm is beeping at two in the morning due to a low battery.
So when should you install your alarm? Summer is a good time since most carbon monoxide accidents happen in the winter due to poorly vented heating systems.
Lastly, how many should you install? Although building codes determine where you must place a smoke detector, the detector placement is governed by manufacturer recommendation (so read the box).
For more information you can take a look at this FAQ.