What's the difference between a PIR motion sensor and an mmWave presence sensor?

PIR (passive infrared) sensors like the Philips Hue and Aqara P1 detect movement by sensing heat changes, so they're reliable, battery-friendly, and cheap, but they can miss a person sitting still. mmWave radar sensors like the Aqara FP2 and FP1E detect tiny movements and even a stationary body, enabling true 'presence' automations, but they're pricier, usually need wired power, and verified-purchase reviewers report a steeper setup curve.