Wake-up Receivers (WuRs) represent one of the most promising solutions for allowing an ultra low power consumption in wireless sensor networks. However, WuRs have several limitations such as low sensitivity, inducing a miss-interpret of the wake-up signal, and thus a performance degradation of the whole system. This work introduces two complementary schemes, namely minimum energy coding and preamble filtering, in order to enhance the WuR reliability while being energy efficient. It is shown through experimental measurements an enhancement on the reliability up to 22% and a total energy saving of 42% while applying minimum energy coding. Moreover, a significant reduction of the false wake-up is realized through preamble filtering.