Smoke and Carbon Monoxide detectors
Having smoke and carbon monoxide detectors in the correct place can save your life. To make sure there working we recommend inspecting them at least twice a year. To inspect them first make sure they are in the proper place. There should be one smoke alarm in every bedroom, and a minimum of one smoke and carbon monoxide detector per floor. There must also be one smoke and carbon monoxide detector outside every bedroom area (The detector in the hallway could be a smoke and carbon monoxide combo).
Once you have determined their placement, we need to check their age. Smoke alarms are designed to last for around 10 years. Most new detectors come with a place to write an install date, check if it was filled in. If not, most manufacturers make the plastic housing out of a material that turns yellow after about 10 years, so if it has a yellow tinge to it, it's very likely time to replace it. If you can't tell from the past 2 tricks, use a little common sense, if it looks like it belongs in a museum, it's probably time to replace it. It's also very important to make sure the detector is not painted or covered, as it can stop it from working.
Once all that is confirmed you can move on to the fun part. Push the test button on the alarm and make sure it works. You may have to hold it for a couple of seconds depending on the brand. (its always a good idea to look up your brands testing instructions, as every brand is slightly different)
If the test fails you can try replacing the battery. newer alarms are sealed and have a built-in 10-year battery. replacements can be bought on amazon, most hardware stores, Costco, etc.