Couple of other thoughts. If you loose your only key, and the car is locked, you've got a big problem. I took my key to a local locksmith who had the same key blank that Lambo uses (it's used on a number of other cars as well) in stock and was able to duplicate my key for about twenty bucks. The key won't start the car without a properly programmed fob, but it will open the door and turn the car on. You may find a good hiding place for it under the car.
If you can't unlock the car using the buttons on the fob because of a dead battery in the fob or in the car, you can open the door with the real key or the key blank if you have one made. Problem is, when you try to slide the tab down that covers the door lock, you've got about a 90% chance of breaking it. You can't just buy the tab separately, but will need to buy the entire handle assembly which will then need to be painted and installed from inside the door. The other option is to glue the tab back into place or use velcro or something on it. Best advice - Avoid getting in to a situation where using the door lock is the only option by changing the fob battery every year and not forgetting to turn of the lights when you park the car. If you've got a weak battery and will be leaving the car, consider keeping the drivers window down.
The dead car battery issue is a concern. Most folks have a trickle charger they connect to the battery, but the connection cable and charger are usually kept in the trunk. If the battery dies and the car is locked, the've gotten to get the trunk open to begin charging the battery.
I took a different approach. Since you can buy a battery tender at any auto parts store, and since they all use the same type plug to connect to the cable and fuse that is attached to the battery, I just got a longer cable, attached it to the battery and ran it up behind the drivers windshield wiper arm where it is hidden from view, but easily accessible from the exterior of the car.
If I have a dead battery and a locked car, I may be able to get to an auto parts store, buy a new tender and charge the battery. If so I'm back in business. Without this setup, I'd have no way of accessing the battery without opening the door with the mechanical key and likely breaking off the tab while trying to remove it.