No recharge. Change the hole product after 10 years. This seems at the first moment, not to be not a sustainable product. But there is another reason. After so many years, the vents will be dirty an the function isn't sure anymore perhaps. So it make sense to change the hole product for safty reasons. and - this product should be for safty reasons. That was my opinion to buy this product. (there ist an LED to warning about the battery is low)

This means that the warning tone sounds simultaneously on all networked smoke detectors. If, for example, smoke develops in the living room, it can take a relatively long time until enough smoke has come through the closed bedroom door to trigger the smoke detector there as well, but if the smoke detector in the living room and in the bedroom are networked with each other, you may still be able to extinguish the fire yourself, of course only after alerting the fire brigade and the other residents or neighbours.