A user interface system for allowing users to initiate events comprises: a plurality of markers each having a marker identity; a plurality of portable readers each having a reader identity and arranged to read said marker identities from adjacent markers, and at least one base station arranged to communicate with said readers in a wireless manner, wherein at least one reader is provided with actuation means which when actuated by a user causes the reader identity of the reader and the marker identity of an adjacent marker to be transmitted by the reader to said base station, so as to cause, for at least one of said markers, said base station to initiate, directly or indirectly, an action which is at least partly determined by the reader identity of said reader.