The LD2420 24GHz radar presence sensor is designed for indoor projects that need to know whether a person is in a monitored area, including when they are making only small movements. It uses FMCW radar rather than changes in body heat, allowing it to detect normal movement, subtle movement and the small motions made by someone sitting or standing relatively still.
The module provides a straightforward digital presence output alongside a UART interface for reading presence, approximate target distance and radar energy data. Its detection area can be adjusted using configurable distance gates, with separate trigger and hold thresholds to help balance reliable detection against unwanted activations.
The LD2420 uses its own communication protocol and is supported by the ESPHome LD2420 component. Community-developed Arduino libraries are also available (although some limit the sensor's features), however the LD2420is not compatible with software libraries written specifically for the LD2410 family.
Unlike a conventional PIR sensor, radar does not need a warm body to move across distinct detection zones. This makes the LD2420 useful for occupancy sensing in offices, living spaces and work areas where someone may remain seated for an extended period.
Radar can pass through some non-metallic materials and may detect movement outside the intended area. Careful positioning and adjustment of the distance gates and thresholds can help reduce detections through thin walls, doors or enclosures.
The module operates directly from 3.3V and is well suited to ESP32 and other 3.3V microcontroller projects. It comes with a pre-soldered 2.54mm header and is suitable for use with breadboards and jumper wires.
Which presence sensor should I choose?
The LD2410C, LD2410B and LD2420 are all 24GHz radar presence sensors capable of detecting normal movement and the smaller movements made by a relatively stationary person. The main differences are their physical format, supply requirements, configuration options and software compatibility.
The LD2410C is a convenient general-purpose option, with a compact breadboard-friendly layout, Bluetooth configuration and broad support from existing LD2410 Arduino and ESPHome integrations.
The LD2410B provides similar LD2410 sensing and software compatibility in a longer, narrower format, with both pre-soldered and headerless variants available.
The LD2420 (this product) is a separate 3.3V design with its own serial protocol and threshold-based calibration system, making it better suited to projects that specifically require native 3.3V power or its different detection characteristics.
Note: Sensors of this type are often described commercially as “mmWave” sensors. Strictly speaking, 24GHz has a wavelength of approximately 12.5mm, just outside the conventionally defined millimetre-wave range of 10mm to 1mm.
