1. A key device ( 1 ) comprising: a mechanical interface ( 13 ) for mechanically manoeuvring a lock device ( 20 ) upon successful access control, the mechanical interface comprising a connector ( 12 ) for powering the lock device ( 20 ) and for communication with the lock device ( 20 ) such that the lock device ( 20 ) is able to perform electronic access control using the key device ( 1 ); a clock ( 4 ); a memory ( 17 ); a radio communication module ( 6 ); and a controller ( 2 ) arranged to, using the radio communication module ( 6 ) communicate online with an access control device ( 30 ) and use the memory ( 17 ) as temporary storage for offline communication between the access control device and one or more lock devices ( 20 ).