Over the years, I have liberated many devices from their proprietary protocols. The most popular devices I have done this for is for Bluetooth devices. Bluetooth devices are cheap but are limited by range compared to WiFi devices. ESPHome allows making Bluetooth repeaters but to allow the Bluetooth repeaters to repeat signals it needs to know what signal to send. This is why we need to reverse engineer the BLE commands being sent when you press a button on its app.

Why Bother? The Joy of True Control

We’ve all been there. You buy a “smart” device, only to find it locked into its own ecosystem, beholden to a cloud service that might disappear tomorrow. Or worse, it simply doesn’t play nice with your existing Home Assistant setup. That’s where reverse engineering comes in. It’s about breaking free, understanding how these devices truly communicate, and then bending them to your will.

Imagine turning on your Godrej Aer diffuser with a single voice command, or having it automatically activate when you arrive home. This more than convenience, it is true control. It’s about turning passive consumers into active creators of their smart homes.

The Tools of the Trade

Before we start poking and prodding, let’s gather our arsenal. You won’t need anything too fancy, but a few key pieces of software will make your life a whole lot easier:

nRF Connect (Mobile App): This is your primary window into the BLE world. Available for both Android and iOS, it allows you to scan for BLE devices, connect to them, and inspect their services and characteristics. It’s like a digital magnifying glass for Bluetooth signals.

Home Assistant: Your central hub for all things smart home. We’ll be adding our custom BLE controls here.

ESPHome/ESP32: For creating custom firmware for ESP32 boards, allowing them to act as BLE gateways or controllers. This is where the real magic happens for robust, local control.

The Reverse Engineering Process

Our goal is to figure out what specific Bluetooth command - a “characteristic write” in BLE lingo; our device expects to perform an action (like turning on or off). We’ll achieve this by observing the communication when we use the device’s official app.

Step 1: Identify Your Device with nRF Connect

First, power on your Godrej Aer (or whatever BLE device you’re targeting) and open nRF Connect.

Scan for Devices: Tap the “Scan” button. You’ll see a list of nearby BLE devices.

Locate Your Device: Look for your Godrej Aer in the list. It will usually have a recognizable name. Note down its MAC address (e.g., A4:C1:38:DE:D0:BF). This is its unique identifier.

Step 2: Connect and Explore Services/Characteristics

Once you’ve found your device, tap on it to connect. nRF Connect will then display a tree view of its “services” and “characteristics.” Think of services as categories of functionality, and characteristics as specific data points or control points within those categories.

Services: These are usually identified by a UUID (Universally Unique Identifier). Some are standard (like “Device Information”), while others are custom to the manufacturer.

Characteristics: These also have UUIDs and can be read, written to, or subscribed to for notifications. This is where the action happens.

Step 3: Sniffing Out the Command (The Trial and Error Part)

This is often the trickiest part, but also the most rewarding. Your goal is to identify which characteristic, when written to with a specific value, triggers the desired action (e.g., turning on the Godrej Aer).

Look for Writeable Characteristics: In nRF Connect, browse through the services. For each service, expand its characteristics. Look for characteristics that have a “Write” property. These are your prime suspects.

Use the Official App and Observe: This is the most effective method.

Disconnect nRF Connect from the device.

Open the official Godrej Aer app.

In the nRF Connect app, keep an eye on the “Logger” tab (or similar logging feature if available).

Perform the action you want to reverse engineer (e.g., turn on the Godrej Aer) using the official app.

Immediately switch back to nRF Connect and reconnect if it automatically disconnected. In the logger, you might see outgoing write commands.

For the Godrej Aer, after some experimentation and observing the traffic when the official app sends commands, we identify the following:

Service UUID: 6e400000-b5a3-f393-e0a9-e50e24dcca9e

Characteristic UUID (for writing commands): 6e400004-b5a3-f393-e0a9-e50e24dcca9e

Value for "Turn On": [0xBF, 0x62, 0x6D, 0x54, 0x18, 0x68, 0x62, 0x6D, 0x4E, 0x18, 0x9A, 0x62, 0x72, 0x49, 0x00, 0xFF]

This value is a hexadecimal array, which is common for BLE commands. It might look like gibberish, but it’s the specific instruction the device understands.

Step 4: Integrating with Home Assistant (using ESPHome/ESP32)

Now that we have our secret command, let’s put it to good use in Home Assistant. We’ll use an ESP32 board running ESPHome to act as our BLE gateway. This is far more reliable than relying on Home Assistant’s built-in Bluetooth, especially for devices that require active connections.

Prepare your ESP32 with ESPHome:

If you haven’t already, install ESPHome on your ESP32 board. You can find detailed instructions on the ESPHome website.

In your ESPHome configuration file (e.g., esp32_ble_gateway.yaml), add the ble_client component. This allows your ESP32 to connect to other BLE devices.

ble_client:
  - mac_address: A4:C1:38:DE:D0:BF # Replace with your Godrej Aer's MAC address
    id: aer_troys_bedroom # A unique ID for your device

# Add a Template Switch to Control the Device: Next, we'll create a switch in ESPHome that, when toggled, sends our reverse-engineered BLE command.

switch:
  - platform: template
    name: "Aer Button" # This is the friendly name that will appear in Home Assistant
    turn_on_action:
      - ble_client.ble_write:
          id: aer_troys_bedroom # Reference the ID of your BLE client
          service_uuid: 6e400000-b5a3-f393-e0a9-e50e24dcca9e
          characteristic_uuid: 6e400004-b5a3-f393-e0a9-e50e24dcca9e
          value: [0xBF, 0x62, 0x6D, 0x54, 0x18, 0x68, 0x62, 0x6D, 0x4E, 0x18, 0x9A, 0x62, 0x72, 0x49, 0x00, 0xFF]
    # You'll need a turn_off_action if you found a separate command for turning off.
    # If it's a toggle, the turn_on_action might be sufficient for both.
    # For a simple button, you might only need turn_on_action and let the device manage its state.
    # For Godrej Aer, you might need to find the "turn off" command in the same way.

Important Note on turn_off_action: For devices like the Godrej Aer, which might cycle through modes or have a single button press for “on/off,” you’ll need to reverse engineer the “turn off” command in the same way you found the “turn on” command, or understand if the turn_on_action effectively toggles it. For many devices, sending the same command again might simply toggle the state.

Upload to ESP32: Compile and upload this configuration to your ESP32 board using ESPHome.

Integrate with Home Assistant: Once your ESP32 is running the ESPHome firmware, it should automatically appear in Home Assistant under the ESPHome integration. If not, ensure you have the ESPHome integration set up and your ESP32 is on the same network. Your “Aer Button” switch will now be available in Home Assistant!

Beyond the Aer: Tips for Other Devices

The principles we’ve applied to the Godrej Aer are universal for most BLE devices. Here are some extra tips:

Patience is Key: Reverse engineering can be a puzzle. Don’t get discouraged if you don’t find the command immediately.

Manufacturer Apps are Your Friends: Always start by observing the device’s official app. It’s the “ground truth” for how the device expects to be controlled.

Search Online: Before you start from scratch, do a quick search! Someone else might have already reverse-engineered your device and shared their findings. Communities like the Home Assistant forums and GitHub are treasure troves of information.

Notification Characteristics: Some devices send status updates (e.g., battery level, current state) via “notification” characteristics. You can subscribe to these in ESPHome to get feedback from your device.

Bonding: Some BLE devices require “bonding” (a secure pairing process). If you’re having trouble connecting or writing, check if bonding is a requirement. nRF Connect can sometimes initiate bonding.

The Future of Your Smart Home is Open Source

By reverse engineering these devices, you’re not just gaining control over your gadgets; you’re contributing to a larger movement of open-source home automation. You’re turning proprietary black boxes into transparent, controllable components of your home.

So, go forth, connect, observe, and conquer! Your smart home, truly smart, awaits.