A circuit for producing a wake-up signal to control powering up an electronic system, has a frequency selective radio frequency (RF) amplifier circuit that amplifies signals within a predetermined frequency range and produces an amplified RF output signal. An RF detector detects the presence of amplified RF output at the output of the amplifier circuit and produces a signal W indicative of the instantaneous presence of the RF output signal. A threshold detector circuit determines if the amplified output signal has reached a predetermined threshold and produces an output signal T. A clock generates a clock signal having clock period in response to the threshold detector output signal T. A data decoder logic circuit turns off the clock in the absence of an RF output signal for a prescribed time period and decodes the RF detector output signal W into a stream of output signals. A serial comparator circuit compares a most recent stream of N output data signals from the data decoder logic circuit with a stored reference pattern, wherein when the most recent stream of N output logic signals from the data decoder logic circuit matches the stored synchronization pattern the serial comparator circuit generates a wake-up signal that enables power to the electronic system. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.