Wake-up radios enable to achieve theoretical duty cycling limits for the Main RX.; WSNs are a great application area for Wake-up radios but more is yet to come!; There is no magic! You can only get to a certain level with limited power. Pick your battle!; Literature shows that there is still a lot of room to play with such limited power.; System level integration is not trivial.; A low power Wake-up radio design typically needs:; Simple modulation scheme (OOK, FSK, PSK); Avoid quadrature RX; Narrowband RF signal; Step-up input matching network; Free gain!; Supply voltage lower than nominal; Easy way to save power ;Frequency translation; Tuned-RF RX needs too much gain and filtering ;Ring Oscillator based LO generation ;Unless high-Q inductors are available.