An apparatus and method for detecting and logging video outputs from a central control unit (7) to one or more television receivers (4) in which a remote unit (2) in or in proximity to the or each television receiver detects by means of a tuned circuit (5) the horizontal synchronisation signal frequency of the receiver; the detected signal is modulated (6) and fed to the central unit where it is demodulated (8) to produce a signal corresponding to the phase of the receiver horizontal synchronisation signal characteristic of that receiver, the phase of the time synchronisation signal of each of a plurality of video players is compared (24) with the phase of the fed receiver signal to obtain a match and a microprocessor (26) logs the matched signals.
