Thinking you are safe when in reality you are not is VERY dangerous.
Everyone wants to feel safe and secure. A smoke detector is like the Police. Both are there, in the background, waiting to be used. 
Both in your 
mind work perfectly and will never fail you. Did you know you are supposed to change the battery yearly? What if the battery is dead, are you still safe and secure? If you never check the battery and ten years later you find out that the smoke detector was worthless, did you have a great, working smoke detector?
Just because you think you have a great, working smoke detector, does not mean it is actually working! Do you really want to wait until your house is on fire to make sure the battery is fresh and charged? Sometimes you need to open the case and just make sure there is a battery and then push the test button to make sure it works. Lets make sure that The City of Bellaire has working fire detectors and we do not wait until your house is on fire to see that the battery has really been dead for years.