I may well be wrong, but I didn't think cloning was very (if at all) feasible with modern wireless keys. I believe they generate a new public key on each use, so reading one doesn't let you generate the next, as you also need to know the private key for the car as well.
The usual approach is a 'man in the middle' attack, effectively using an 'amplifier' to make the car think the key is close to it, when it is actually still in your house.
That attack is easy to prevent with the ZOE. If you lock the car by pressing the lock button on the key card then it will only unlock by pressing the button again - hands free unlocking is disabled. It's easier to press the button than put your key in a metal box. [I assume the same is true for the ZE50.]