Narrowband smartlocks battery life is about 2 years (4-6 unlocks a day). It will keep notifying you through app when batteries are low, and the lock will also emit a beeping sound when below 10% battery life and the LED lights will flash. If the batteries run out, you can still use metal keys to unlock your door with our locks that have metal key override. (perhaps you can also use your current method of having a spare key with a family or trusted friend).