BLE Car Key Solution

A Bluetooth Low Energy (BLE) system that turns your phone and/or Garmin watch into a car key. An ESP32 wired to your car remote's button acts as a bridge — your phone authenticates over BLE and triggers the remote, unlocking or locking the car.

While designed for automotive use, the system can be adapted to any application requiring a secure BLE-triggered action, such as doors, gates, or other access control systems.
(This is not for keyless ignition/starting.)

Designed for both convenience and security:

• No need to carry physical keys for everyday access
• Lost keys alone cannot unlock the car without the additional authentication layer
• Access can be restored on a new device if your phone or watch is lost, with proper authentication

🛠️ How It Works

The ESP32 sits inside the car, powered from the 12V system via a buck converter. A GPIO pin is wired directly across the car remote's button — no MOSFET or relay needed since both share the same 3.3V supply. When you want to unlock the car, the Flutter app on your phone connects over BLE, completes an HMAC-SHA256 challenge-response handshake using a pre-shared key (PSK), and sends a command. The ESP32 verifies the HMAC and drives the GPIO to simulate a button press on the remote.

🧱 Project Structure

ESP32_Firmware/           ESP32 Arduino firmware (PlatformIO)
ESP32-C3_Firmware/        ESP32-C3 Arduino firmware (PlatformIO)
Android_Flutter_Application/   Flutter mobile app (Android; iOS is untested)
Garmin_Watch_App/          Garmin Watch App (Connect IQ v3.0 or newer required)

🔒 Security

Authentication uses HMAC-SHA256 with a challenge-response protocol:

1. The ESP32 generates a random 16-byte nonce
2. The phone/watch reads the nonce and computes HMAC-SHA256(nonce, PSK)
3. The phone/watch sends the HMAC along with a command byte
4. The ESP32 verifies using constant-time comparison, then rotates the nonce

Additional protections include biometric gating on the phone (fingerprint/face), auto-disconnect timeouts (15s unauthenticated, 5min authenticated), and secure storage for the PSK on both the phone/watch and ESP32.

Important: The firmware ships with a placeholder PSK (CHANGE_ME_before_flashing_32chars!). You must change this before deploying. You can update the PSK over BLE from the app after initial setup.

🖥️ Hardware

• MCU: ESP32-C3 or standard ESP32 (C3 variant is better for low power draw like in vehicle running off battery)
• Power: Car 12V through a buck converter to 3.3V (powers both the ESP32 and the remote)
• Remote: Car remote with a physical button — GPIO wired directly across the button
• No MOSFET needed when the remote runs on the same 3.3V supply as the ESP32

🔌 Wiring Diagram (Single button remote)

Car 12V ──► Buck Converter ──► 3.3V ──┬──► ESP32 VIN
                                       └──► Remote (replaces batteries)

ESP32 GPIO 4 ──► Remote button (non-supply leg)
                  Remote button (other leg) ──► 3.3V or GND (depends on remote)

🔄 Button Polarity

Use a multimeter to check which side of the remote's button connects to the supply rail:

• One leg on 3.3V: The button pulls the encoder input HIGH when pressed. Set BUTTON_ACTIVE_HIGH true.
• One leg on GND: The button pulls the encoder input LOW when pressed. Set BUTTON_ACTIVE_HIGH false.

Wire GPIO 4 to the other leg (the encoder input side).

Note: If your remote operates at a different voltage than 3.3V, you'll need a relay or N-Channel MOSFET (e.g. BS170) between the GPIO and the button, plus a separate regulator for the remote.

🚀 Getting Started

💻 ESP32 Firmware

Requirements: PlatformIO (CLI or VS Code extension)

1. Open ESP32_Firmware/ in PlatformIO
2. Edit src/car_unlock_firmware.ino and change DEFAULT_PSK to your own secret (32+ characters recommended)
3. Optionally adjust BUTTON_GPIO, BUTTON_ACTIVE_HIGH, BUTTON_PULSE_MS, BLE_DEVICE_NAME, and other configuration constants at the top of the file
4. Build and flash:

   pio run -t upload
   

5. Monitor serial output:

   pio device monitor
   

📱 Android App (Flutter)

Requirements: Flutter SDK (3.0+)

1. Navigate to Android_Flutter_Application/
2. Install dependencies:

   flutter pub get
   

3. Run on a connected device:

   flutter run
   

On first launch, set the PSK in the app's settings to match what you flashed onto the ESP32.

⌚ Garmin Watch App

Note: PSK needs to be set before compiling app.

📡 BLE Service Details

Characteristic	UUID (suffix)	Properties	Purpose
Challenge	...7891	Read, Notify	16-byte random nonce
Command	...7892	Write	1-byte command + 32-byte HMAC
Status	...7893	Read, Notify	Result of last operation
PSK Update	...7894	Write	Change PSK (requires auth first)

Service UUID: a1b2c3d4-e5f6-7890-abcd-ef1234567890

Commands

• 0x01 — Authenticate only (no button press)
• 0x02 — Authenticate and press remote button

Note: Additional commands will be needed for multi button remotes or additional triggers.

🧰 Configuration

Key constants in car_unlock_firmware.ino:

Constant	Default	Description
DEFAULT_PSK	CHANGE_ME_before_flashing_32chars!	Pre-shared key (change before flashing)
BUTTON_GPIO	4	GPIO pin wired to remote button
BUTTON_ACTIVE_HIGH	true	true if button connects to VCC, false if to GND
BUTTON_PULSE_MS	300	Button press duration in ms
DEBUG_LED_ENABLED	defined	Comment out to disable debug LED
DEBUG_LED_GPIO	2	GPIO for debug LED (active during button press)
BLE_DEVICE_NAME	BLE-Device	BLE advertised name
MAX_CONNECTIONS	3	Simultaneous BLE connections
BLE_TX_POWER	3	TX power in dBm (-12 to 9)
UNAUTH_TIMEOUT_SEC	15	Auto-disconnect for unauthenticated clients
AUTH_TIMEOUT_SEC	300	Auto-disconnect for authenticated clients

📜 License

This project is licensed under the MIT License. See LICENSE for details.