Quote "All you need to do to check if your detector is working or if the batteries are still working (providing the detector has NOT been modified which could affect its integrity), is to simply press the 'test' button or the 'press to reset/test' - whatever your detector says "
I may be wrong (but I do not think so) but pressing the TEST button simply tests that the electronic circuitry is working, it does NOT test the actual sensor itself.
As the sensor has a life expiry limit that is why the whole unit should be replaced every 10 years.