the invention refers to a computer system , comprising : a computer , and a peripheral device , wherein the computer comprises one or more receivers for receiving signals sent from the peripheral device , and a peripheral device movement detector for detecting a movement of the peripheral device from the signals received from the peripheral device . further , the invention referes to a mobile telephone , comprising a device movement tracking member , e . g ., a rollerball . in addition , the invention refers to a computer system , comprising : a mobile telephone comprising a device movement tracking member , and a computer connectable to the mobile telephone , e . g . via a wireless rf connection .