I don't know which office I can use
If you do not have an office, the ALICE secretariat will propose you to use a burotel (shared common space for short stay period at CERN). The key is available at the secretariat and will have to be returned on your last day at CERN.
I know the number of my office
If you know your office number, please fill in the EDH form "Keys & cylinders". Tu budget code to be indicated is 31509. Upon approval of your request, the key will be available at building 55. You can keep the key as long as your contract is active.