ESP32 & Home Assistant: Building a Presence Sensor with mmWave

Traditional PIR (Passive Infrared) motion sensors have been the go-to solution for detecting movement in smart homes for years. But they have limitations: they only detect motion, not presence. They can't tell if someone is sitting still in a room, leading to lights turning off while you're reading or working.

mmWave (millimeter wave) radar sensors solve this problem. Using radar technology similar to what's in modern smartphones, these sensors can detect both motion and static presence—knowing when someone is in a room even if they're not moving. Combined with an ESP32 microcontroller and Home Assistant, you can build a presence detection system that's more accurate and reliable than anything you can buy off the shelf.

Why mmWave Over PIR?

PIR Sensor Limitations

Motion-Only Detection:

Triggers only when movement occurs
Can't detect stationary people
Prone to false positives (pets, sunlight)
Limited range and field of view
Slow response time

Real-World Problems:

Lights turn off while you're sitting at a desk
False triggers from heating vents
Misses slow movements
Doesn't work well in corners

mmWave Advantages

Presence Detection:

Detects both motion and static presence
Knows when someone is in a room, even if still
More accurate occupancy detection

Better Performance:

Faster response time
Wider detection range
More reliable in various conditions
Less prone to false positives
Works through thin materials (drywall, glass)

Advanced Features:

Distance measurement
Multiple target detection
Movement speed detection
Configurable sensitivity

Electronics components on breadboard — ESP32 and sensor components

Understanding mmWave Technology

mmWave radar operates in the 24GHz or 60GHz frequency bands, using radio waves to detect objects. Unlike PIR sensors that detect heat, mmWave sensors detect the reflection of radio waves, allowing them to:

Detect stationary objects (people sitting still)
Measure distance to targets
Detect movement speed and direction
Work regardless of ambient temperature

LD2410 Sensor Overview

The HiLink LD2410 is one of the most popular mmWave sensors for DIY projects:

Specifications:

Frequency: 24GHz
Detection Range: 0.75m to 6m (configurable)
Detection Types: Motion and presence
Update Rate: Up to 100Hz
Interface: UART (serial)
Power: 5V, ~100mA
Size: Compact module (~30mm × 20mm)

Features:

Motion detection (moving targets)
Presence detection (stationary targets)
Distance measurement
Configurable sensitivity zones
Multiple target detection

Hardware Requirements

Components Needed

Essential:

ESP32 development board (ESP32-WROOM-32 or similar)
LD2410 mmWave sensor module
USB cable for programming
Jumper wires (Dupont wires)
5V power supply (USB power bank or wall adapter)

Optional but Recommended:

Breadboard for prototyping
3D printed enclosure
Status LED
Resistors (for LED if used)

ESP32 Board Options

ESP32-DevKitC:

Good for prototyping
Built-in USB-to-serial
Easy to program
Price: $5-10

ESP32-WROOM-32:

Compact module
Requires external USB adapter
Smaller form factor
Price: $3-8

ESP32-S3:

More powerful
Better for complex projects
Overkill for this project
Price: $8-15

Wiring the LD2410 to ESP32

The LD2410 communicates via UART (serial). Here's the wiring:

LD2410          ESP32
------          -----
VCC      →      5V (or 3.3V with level shifter)
GND      →      GND
TX       →      GPIO 4 (RX on ESP32)
RX       →      GPIO 5 (TX on ESP32)
OUT      →      (Optional) GPIO 2 (for direct output)

Important Notes:

LD2410 operates at 5V logic levels
ESP32 GPIO pins are 3.3V
LD2410 TX can typically drive ESP32 RX directly (3.3V tolerant)
For LD2410 RX, use a level shifter or voltage divider (or use 3.3V if your module supports it)

Simplified Wiring (if LD2410 is 3.3V compatible):

LD2410          ESP32
------          -----
VCC      →      3.3V
GND      →      GND
TX       →      GPIO 4
RX       →      GPIO 5

Software Setup: ESPHome

ESPHome is the easiest way to integrate ESP32 devices with Home Assistant. It provides a simple YAML-based configuration system.

Installing ESPHome

Option 1: Home Assistant Add-on (Easiest)

In Home Assistant, go to Settings → Add-ons
Add-on Store → ESPHome
Install and start ESPHome
Open Web UI

Option 2: Docker

docker run -d \
  --name esphome \
  --restart unless-stopped \
  -v /path/to/esphome:/config \
  -p 6052:6052 \
  esphome/esphome

Option 3: Python (pip)

pip install esphome
esphome dashboard /path/to/config

Creating the ESP32 Configuration

Create a new device in ESPHome:

esphome:
  name: presence-sensor-bedroom
  platform: ESP32
  board: esp32dev
  framework:
    type: arduino

wifi:
  ssid: "YourWiFiSSID"
  password: "YourWiFiPassword"
  
  # Enable fallback hotspot
  ap:
    ssid: "Presence Sensor Fallback"
    password: "fallback123"

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "your-encryption-key-here"

# OTA updates
ota:
  - platform: esphome
    password: "your-ota-password"

# Web server for status
web_server:
  port: 80

# UART for LD2410
uart:
  tx_pin: GPIO5
  rx_pin: GPIO4
  baud_rate: 256000

# LD2410 BLE and Radar sensor
ld2410:
  timeout: 150ms
  # Optional: Configure detection zones
  max_move_distance: 6m
  max_still_distance: 4m
  g0_move_threshold: 10
  g0_still_threshold: 10

# Binary sensors for motion and presence
binary_sensor:
  - platform: ld2410
    has_target:
      name: "Bedroom Motion"
    has_moving_target:
      name: "Bedroom Moving Target"
    has_still_target:
      name: "Bedroom Still Target"

# Sensor for distance
sensor:
  - platform: ld2410
    moving_distance:
      name: "Bedroom Moving Distance"
    still_distance:
      name: "Bedroom Still Distance"
    detect_distance:
      name: "Bedroom Detect Distance"
    move_energy:
      name: "Bedroom Move Energy"
    still_energy:
      name: "Bedroom Still Energy"

# Status LED (optional)
status_led:
  pin:
    number: GPIO2
    inverted: true

Compiling and Flashing

Compile the firmware:
- Click "Install" in ESPHome
- Select "Plug into this computer"
- Flash over USB
Or use OTA (Over-The-Air):
- Connect ESP32 to WiFi first (via USB)
- Then use OTA for future updates
- No need to physically access device

Home Assistant Integration

Automatic Discovery

If ESPHome is properly configured, the device will automatically appear in Home Assistant:

Go to Settings → Devices & Services
Look for "ESPHome" integration
The presence sensor should appear automatically
Entities will be created for each sensor

Manual Configuration

If automatic discovery doesn't work, add manually:

# configuration.yaml
esphome:
  name: presence-sensor-bedroom
  platform: ESP32
  # ... rest of config

Using the Sensors in Automations

Basic Presence Detection:

automation:
  - alias: "Turn on lights when presence detected"
    trigger:
      - platform: state
        entity_id: binary_sensor.bedroom_still_target
        to: "on"
    action:
      - service: light.turn_on
        target:
          entity_id: light.bedroom_lights

  - alias: "Turn off lights when no presence"
    trigger:
      - platform: state
        entity_id: binary_sensor.bedroom_still_target
        to: "off"
        for:
          minutes: 5
    action:
      - service: light.turn_off
        target:
          entity_id: light.bedroom_lights

Advanced: Motion vs Presence:

automation:
  - alias: "Bright lights on motion"
    trigger:
      - platform: state
        entity_id: binary_sensor.bedroom_moving_target
        to: "on"
    action:
      - service: light.turn_on
        target:
          entity_id: light.bedroom_lights
        data:
          brightness: 255

  - alias: "Dim lights for presence"
    trigger:
      - platform: state
        entity_id: binary_sensor.bedroom_still_target
        to: "on"
        from: "off"
    condition:
      - condition: state
        entity_id: binary_sensor.bedroom_moving_target
        state: "off"
    action:
      - service: light.turn_on
        target:
          entity_id: light.bedroom_lights
        data:
          brightness: 128

Advanced Configuration

Fine-Tuning Detection Zones

The LD2410 allows you to configure detection zones:

ld2410:
  timeout: 150ms
  max_move_distance: 6m      # Maximum distance for motion detection
  max_still_distance: 4m     # Maximum distance for presence detection
  g0_move_threshold: 10      # Sensitivity zone 0 (0-0.75m) motion
  g0_still_threshold: 10     # Sensitivity zone 0 presence
  g1_move_threshold: 20      # Zone 1 (0.75-1.5m)
  g1_still_threshold: 20
  g2_move_threshold: 30      # Zone 2 (1.5-2.5m)
  g2_still_threshold: 30
  g3_move_threshold: 40      # Zone 3 (2.5-4m)
  g3_still_threshold: 40
  g4_move_threshold: 50      # Zone 4 (4-6m)
  g4_still_threshold: 50

Tuning Tips:

Start with default values
Increase thresholds to reduce sensitivity
Decrease thresholds to increase sensitivity
Test in your actual environment
Adjust zone-by-zone based on room layout

Multiple Sensors

For larger rooms, use multiple sensors:

# Sensor 1 - Room entrance
esphome:
  name: presence-sensor-bedroom-entrance
  # ... config with different GPIO pins

# Sensor 2 - Room center  
esphome:
  name: presence-sensor-bedroom-center
  # ... config

Combine in Home Assistant:

template:
  - binary_sensor:
      - name: "Bedroom Any Presence"
        state: >
          {{ is_state('binary_sensor.bedroom_entrance_still_target', 'on') or
             is_state('binary_sensor.bedroom_center_still_target', 'on') }}

Enclosure and Installation

3D Printed Enclosure

Design considerations:

Allow airflow (sensor can get warm)
Mounting options (wall, ceiling)
Cable management
LED visibility (if using status LED)

Popular Designs:

Search Thingiverse for "LD2410 enclosure"
Many designs available for ESP32 + LD2410
Choose based on mounting preference

Installation Tips

Mounting Location:

Ceiling mount: Best coverage, detects entire room
Wall mount: Good for specific areas
Corner mount: Maximizes detection range
Height: 2-3 meters (6-10 feet) recommended

Orientation:

Sensor should face the area to monitor
Avoid pointing at windows (can detect outside)
Consider furniture placement
Test before permanent installation

Power:

USB power bank: Portable, good for testing
Wall adapter: Reliable for permanent install
PoE (with adapter): Professional installation
Battery (with ESP32-S3): Truly wireless (advanced)

Troubleshooting

Sensor Not Detecting

Check Wiring:

Verify all connections
Check power (5V for LD2410)
Test with multimeter
Try different GPIO pins

Check Configuration:

Verify UART pins match wiring
Check baud rate (256000 for LD2410)
Review ESPHome logs
Test with serial monitor

Environmental Factors:

Metal objects can interfere
Thick walls block detection
Test in different locations
Adjust sensitivity thresholds

False Positives

Reduce Sensitivity:

Increase threshold values
Reduce detection distance
Adjust zone-specific thresholds
Add delay before triggering

Filter in Home Assistant:

template:
  - binary_sensor:
      - name: "Bedroom Presence Filtered"
        state: >
          {{ is_state('binary_sensor.bedroom_still_target', 'on') }}
        delay_on: 00:00:05  # 5 second delay

Connection Issues

WiFi Problems:

Check signal strength
Use 2.4GHz (ESP32 doesn't support 5GHz)
Reduce distance to router
Check ESPHome logs

Home Assistant Not Seeing Device:

Verify API encryption key matches
Check firewall settings
Ensure ESPHome add-on is running
Restart Home Assistant

Use Cases and Applications

Room Occupancy Automation

Smart Lighting:

Turn on when presence detected
Dim when stationary presence
Turn off after timeout
Different scenes for motion vs presence

Climate Control:

Adjust HVAC based on occupancy
Turn off when room empty
Set different temps for occupied/unoccupied

Entertainment Systems:

Pause media when room empty
Adjust volume based on presence
Turn on TV when motion detected

Security Applications

Intrusion Detection:

Alert on unexpected presence
Monitor specific zones
Integrate with security system
Record events in Home Assistant

Energy Efficiency

Power Management:

Turn off devices when room empty
Reduce heating/cooling for unoccupied rooms
Smart power strips based on presence
Monitor occupancy patterns

Comparison: mmWave vs Other Sensors

Sensor Type	Motion	Presence	Range	Cost	Complexity
PIR	Yes	No	5-10m	$	Low
mmWave	Yes	Yes	6m+	$$	Medium
Ultrasonic	Yes	Limited	3-5m	$	Medium
Camera	Yes	Yes	Variable	$$$	High
ToF	Yes	Limited	2-4m	$$	Medium

mmWave Advantages:

Best presence detection
Privacy-friendly (no camera)
Good range
Reasonable cost
Works in darkness

Conclusion

Building a presence sensor with ESP32 and mmWave technology gives you capabilities that commercial sensors can't match at a fraction of the cost. The LD2410 sensor, combined with ESPHome and Home Assistant, creates a powerful, customizable presence detection system.

Key benefits:

Accurate presence detection: Knows when someone is in a room, even if still
Privacy-focused: No cameras, radar-based detection
Customizable: Fine-tune for your specific needs
Cost-effective: ~$15-20 total cost
Integrates seamlessly: Works with Home Assistant ecosystem

Whether you're automating lights, optimizing energy usage, or building a comprehensive smart home, mmWave presence sensors are a significant upgrade over traditional PIR sensors. The combination of ESP32's flexibility and mmWave's accuracy makes this a perfect project for any smart home enthusiast.

For more ESP32 projects and tutorials, check out Random Nerd Tutorials' ESP32 guide and the ESPHome documentation for advanced configurations.