Accurate and scalable localization is one of the keys to pervasive interaction with the Internet of Things. mmWave backscatter possesses great potential toward this goal - The abundant bandwidth of mmWave enables high-precision localization, and low-cost and ultra low-power backscatter tags enable massive deployment with minimum deployment cost and maintenance efforts. We present Hawkeye, a new mmWave backscatter that offers (i) submillimeter localization accuracy (ii) at over 2 m range, (iii) while consuming 2.25 μW power. At the heart of our design is the new Hawkeye super-resolution, which exploits the interplay between the tag FSK and FMCW radar to improve the localization performance by ×60 over conventional FMCW radar (i.e., c/2BW). Hawkeye readers were implemented on commodity 77 GHz radars and the tags were prototyped on PCB.