Both are non-visual RF sensors. The tradeoff is dedicated ranging hardware vs commodity WiFi reuse.
RF front-end
mmWave radar uses a purpose-built transceiver (typically 60 GHz) with chirp modulation designed for range-Doppler processing. Resolution: centimeter-range distance, sub-Hz Doppler for micro-motion.
WiFi CSI uses the existing 2.4/5 GHz WiFi PHY. Resolution: limited by wavelength (~6 cm at 5 GHz) and packet-rate sampling. Fine-ranging is not the design goal.
Fine-motion SNR
Radar front-ends are optimized for detecting sub-millimeter chest displacement — breathing and heartbeat are first-class signals. ESP32 CSI can detect breathing after phase sanitization, but the hardware noise floor is higher and SNR is placement-dependent.
For clinical-grade vitals, radar wins. For presence awareness (“someone is still in the room”), CSI is often sufficient.
Cost and scale
| mmWave radar module | ESP32 CSI node | |
|---|---|---|
| Unit cost | $10–50+ per module | $3–8 per module |
| Dedicated hardware | Yes — radar in every zone | Reuses existing WiFi infrastructure |
| OTA upgrade | Module-specific | Standard ESP32 firmware |
| Ecosystem | Smaller, vendor-specific | Huge (Home Assistant, MQTT, etc.) |
Covering a 10-room office with radar means 10+ dedicated modules. With CSI, a few nodes per room on hardware you may already have deployed for other purposes.
When to choose which
mmWave radar: per-zone ranging, fall detection with low false-alarm requirements, vital signs in a clinical-adjacent setting, single-room precision.
WiFi CSI: whole-building occupancy at scale, multi-room analytics, smart-home presence holds, security zone detection — anywhere economics and ubiquity matter more than centimeter ranging.
See presence detection for CSI micro-motion scope.