A 915-MHz energy-enhanced wake-up receiver (EE WuRx) is proposed for wireless energy-harvesting (WEH) systems based on a modified legacy device. With the presented frequency-hopping two-tone modulation (FH TTM), the receiver converts the in-band harvesting energy (HE) from the legacy device into the data power with reduced constraint to the HE frequency. Fabricated in a 65-nm CMOS process, the proposed wake-up receiver (WuRx) achieves a −90-dBm EE sensitivity when receiving a continue-wave (CW) energy of −25 dBm and gives a sensitivity improvement of 26.4 dB compared with the case without HE, while consuming at a 5-kb/s data rate. Upon the −90-dBm EE sensitivity, the WuRx performs 46.5- and 22-dB tolerances to a 100-kb/s amplitude-modulated (AM) blocker and an 8-MS/s quadrature-AM blocker, respectively.