When a Fire extinguisher has reached the end of it's life span, and can't be recharged or was used for some reason it needs to be disposed of properly. It should not be put in the trash, but should be taken to the Household Hazardous Waste Collection drop-off for recycling.
The maximum life of any smoke detector is 10 years. It could start acting inappropriately before that time and then assume it has reached is usefulness. When you are disposing of these keep in mind some have a very small amount of radioactive material. They should be disposed of properly. The Household Hazardous Waste Collection drop-off will accept them and recycle what they can.
Carbon Monoxide detectors (CO detectors)
They have a life span of 5 years. When they are outdated they should be taken to the Household Hazardous Waste Collection drop-off for recycling.