A technique for on-demand power wake up for digital signage includes providing 400 a detector operable to detect an envelope of a digital signal, receiving 402 an extended length packet by the detector, wherein the packet consists of a same, repeated data symbol, detecting 404 the extended length packet in the detector to provide an output signal, comparing 406 the output signal against a reference threshold, and providing 410 a wake up signal if the output signal exceeds the reference threshold. This can then be followed by receiving 416 information to display on the sign.