This paper presents an ultra-low power (ULP) high sensitivity binary frequency-shift keying (BFSK) direct conversion receiver (RX) for the internet of things (IoT). By employing a combination of a 2-stage ring voltage-controlled oscillator (VCO) and a 50 %-to-25 % duty conversion passive mixer, the power consumption is dramatically reduced. The prototype of the proposed RX which is implemented in a 55 nm CMOS technology shows −99 dBm sensitivity for 915 MHz 100 kbps BFSK signal while dissipating 499 µW from 0.9 V supply.