A wake-up system includes an instigator for transmitting a wake-up message from a primary node to a receiver at a secondary node. The instigator sends a wake-up on either first RF channel or a second RF channel having respective frequencies such that the second RF channel is an image of the first RF channel at a local oscillator frequency of the receiver. The receiver includes an RF filter that passes both the image and non-image channels, a frequency generator for generating a local oscillator signal at the local oscillator frequency, and a mixer for mixing the filtered modulated RF signal with said local oscillator signal to generate a modulated intermediate frequency (IF) signal. The receiver monitors both the image and non-image channels simultaneously for a valid wake-up message. A wake-up message detector indicates a wake-up condition in response to the reception of a valid wake-up message.