Fermion: C4002 mmWave Human Presence Sensor - Static & Motion Detection for Home Assistant (10m)

The Fermion: C4002 is a 24GHz FMCW mmWave human presence sensor designed to accurately detect moving, stationary, and micro-motion targets. Built as a reliable alternative to traditional PIR sensors, it integrates smoothly with ESP32 microcontrollers, Arduino, and Home Assistant. It is ideal for makers and smart home enthusiasts looking to build responsive lighting, climate control, and privacy-friendly occupancy automations.

True presence micro-motion detection

Utilising 24GHz FMCW radar technology, the module detects subtle chest expansion and breathing movements. This resolves standard PIR limitations by preventing smart lighting and climate systems from turning off while occupants are sitting still, reading, or sleeping.

Streamlined Home Assistant integration

The module interfaces with ESP32 controllers over a standard UART connection and is fully supported by ESPHome. Flashing with verified YAML configurations immediately exposes Occupancy, Distance, and Energy entities within Home Assistant.

Wide static and motion coverage

Featuring a 120-degree by 120-degree field of view, the sensor covers a 10 by 10 metre area. It detects active motion such as walking up to 11 metres and static micro-motion up to 10 metres.

Configurable detection boundaries

Software-adjustable distance thresholds allow users to confine monitoring to specific functional areas like desks or sofas. This prevents unwanted triggers from adjacent hallways and stops radar signals from penetrating thin partition walls.

Adaptive background noise filtering

The C4002 establishes an adaptive environmental noise baseline to filter out non-human interference like moving curtains or swaying plants. This intelligent filtering ensures automations only trigger in the presence of real human occupants.

Compact hardware and versatile specifications

Measuring just 22mm by 26mm, the sensor operates between 3.6V and 5.5V and includes integrated 0 to 50 lux ambient light detection. It offers both UART and configurable digital IO outputs, operating across a wide temperature range from -20 to 85 degrees Celsius.

Downloads & documentation

• Product wiki (DFRobot)