1b. That's the most expensive let-in-a-neighbour idea ever. My neighbours have a spare key to my place. If you're going to trust them once, why not just trust them?
2. Again .. a really expensive solution to this simple problem. How often do you actually leave your door unlocked? Or are you just scared and this device will give you needless peace of mind?
3. The point is that this device lets you unlock from anywhere in the world. Why would you unlock it from anywhere other than your house?
4. What if the neighbour in 1b decides to use the knob lock (after all, it's his habit to lock) and you left your keys at home because you have your phone?