Many owners aren't aware that their Smart Keys have a built-in removable hard key. But it's there in different forms depending on the make and model of the car. The key is a good old fashioned flat metal key that's cut to fit your car's door, trunk, and glove box locks. Great, but what is an old school key doing in a 21st century smart key? Well, it's there for backup purposes. Just in case your smart key stops working for some reason and won't open the doors for you. If this happens, remove the key from your remote and insert it into the little lock cylinder in your door handle and voila, you're in. If you have push button keyless start, you may not be able to start your car, however. But at least you can get in and call for help.
In some smart keys, the key has a hole with a ring in it which you can attach to your main key ring. This also enables you to remove your remote from the rest of your keys, which is handy (and safe) to do when valet parking.
Refer to your owners manual for the location of the release button on your remote and the location of the lock cylinders on your car.