The battery drops in to your existing 120v smoke detectors as the backup battery. It still chirps when the battery is low. It still operates normally. The ad

The battery drops in to your existing 120v smoke detectors as the backup battery. It still chirps when the battery is low. It still operates normally. The added benefit is that it can alert you to an alarm if you are away from home. If your smoke detectors are all wired together you probably only need one of these. But yes the disposable nature of the product is a concern for e-waste, convenience, and cost.