— This paper reviews proposed realization concepts and achievements of wireless sensor nodes and focuses on new developments in the 24 GHz frequency range. The relatively high frequency offers the advantage of ultra miniaturization and therefore opens new application fields. On the other hand power consumption of the RF-front-end becomes still more challenging than at lower frequencies. It is shown that by applying very simple CMOS transceiver architectures and modulation schemes combined with innovative efficient wake-up concepts, very low energy consumption can be achieved. Technological realization concepts and first experimental results from a 24 GHz demonstrator as well as novel special purpose wakeup-circuitry are presented, too.