A low power method and apparatus for detecting wake-up signals in sniff processing performed in an implantable medical device (IMD) using a staged detection of RF energy in signals received in order to conserve current consumption. Incoming signals are monitored in a plurality of detection stages which each incrementally increase the accuracy of detecting whether the received signal is a wake-up communication signal. A desired number of stages of signal quantity measurements are performed such that a combined signal quantity is calculated by updating the signal quantity measurements performed in prior stages with signal quantity measurements performed at each stage. The combined signal quantity of the received communication signal is compared at each detection stage against a corresponding threshold value for that stage. The staged detection process aborts sniff processing if the combined signal quantity fails to meet the corresponding threshold value for that stage.
