Airport luggage lockers

A question about the luggage Lockers at Brussels airport
http://www.brusselsairport.be/en/passngr/services/luggage_lockers/
Does anybody know if they work with a code or with a key, or how? It is for somebody to leave a car key (the car will be in the airport car park) there for me to pick up three days later.
Or is there another way of doing this? I don't have a duplicate of the key ...