Panic sound

You likely have one of the doors or the hatch not fully closed, or another smart key inside the car.
If you cannot lock the car by using the lock button on the remote, one of the doors or hatch is not fully closed.
If you can lock the car by using the lock button on the remote, there is another smart key somewhere inside the car.
Another way to check for a smart key lost inside the car is to go in the car without carrying your smart key and try to start the car. If it starts, there is another smart key somewhere inside the car.