When was the last time you checked to see if your smoke detectors were working properly? According to Consumer Reports, the life expectancy of smoke alarms is generally 10 years, after which point their sensors can begin to lose sensitivity. The test button only confirms that the battery, electronics, and alert system are working; it doesn’t mean that the smoke sensor is working. To test the sensor, use an aerosol can of smoke alarm test spray that simulates smoke. But even if the 17-year-old smoke alarms in your homes can still detect smoke, we recommend replacing them with new models.