a system for delivering and displaying messages in a display device part of a network comprising : a set of display devices and a set of presence detection sensors configured to provide a sensor state which is related to the presence of users . each of the display devices is configured to periodically sense the sensor states of a subset of said presence detection sensors . each of the display devices is configured to compute a presence probability estimate , function of said sensor states , and whose value covariates with the probability that a user is in a neighbour area of said display device . each display device is configured to display messages whose presence probability estimate is above a predetermined threshold .