Is the C4002 worth it over a PIR sensor?

Yes if you need to detect people who are still, such as someone reading or working at a desk. PIR only catches motion, so it drops presence when a person stops moving. The C4002 costs more and needs UART setup.

Does it work with Arduino or ESP32?

Yes. It runs on 3.6–5.5V and uses UART, so a 3.3V ESP32 or 5V Arduino can drive it. You need to match logic levels and write or load code to read the serial output.

Can it detect someone through a wall or enclosure?

It works through plastic and glass, which suits enclosures and lamp housings. It is not a through-wall sensor; dense walls and metal block the radar.

What is the difference between the UART and OUT pins?

UART gives full data and configuration, including presence and distance information. The OUT pin is a simple high/low trigger you can wire to a relay or microcontroller input without parsing serial data.

What comes in the box?

The module itself, typically with a connecting cable. A controller, power supply and housing are not included, so plan for those in your build.

Watch for sales at maker-electronics stores and compare listings across retailers. Prices vary by store and stock, so check the current price history before buying.

DFRobot

Fermion: C4002 mmWave Human Presence Sensor

Last price we saw

$9.90at Amazon, last seen Oct 31

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Our take on the Fermion: C4002 mmWave Human Presence Sensor

The DFRobot Fermion C4002 is a 24GHz mmWave radar module that detects human presence, including people who are sitting still, rather than only motion. It covers up to 11m at a 120° × 120° angle, runs on 3.6–5.5V, and talks over UART with a configurable OUT pin plus a 0–50 lux light sensor. It is a bare module for makers and product builders, not a finished smart-home device, so expect wiring and code. No current price was supplied, so compare store listings before buying.

Best forMakers building presence-aware lighting or HVACESP32 and Arduino projects needing still-body detection