When things don’t seem to be working right, here are some things to try.

Enable Logging

The easiest way to enable logging is to set the BLEAK_LOGGING environment variable. Setting the variable depends on what type of terminal you are using.

Posix (Linux, macOS, Cygwin, etc.):


Power Shell:


Windows Command Prompt:


Then run your Python script in the same terminal.

Capture Bluetooth Traffic

Sometimes it can be helpful to see what is actually going over the air between the OS and the Bluetooth device. There are tools available to capture HCI packets and decode them.

Windows 10

No special software is required on Windows to capture Bluetooth traffic, however special software is required to convert it to a useful format.


To capture Bluetooth traffic:

  1. Open a Command Prompt as Administrator.

    • Search start menu for cmd.

    • Right-click Command Prompt and select Run as Administrator.

      Screenshot of Windows Start Menu showing Command Prompt selected and context menu with Run as Administrator selected.
  2. Run the following command in the Administrator Command Prompt:

    logman create trace "bth_hci" -ow -o C:\bth_hci.etl -p {8a1f9517-3a8c-4a9e-a018-4f17a200f277} 0xffffffffffffffff 0xff -nb 16 16 -bs 1024 -mode Circular -f bincirc -max 4096 -ets


    C:\bth_hci.etl can be replaced with any file path you like.

  3. Run your Python script in a different terminal (not as Administrator) to reproduce the problem.

  4. In the Administrator Command Prompt run:

    logman stop "bth_hci" -ets


Microsoft no longer has tools to directly view .etl files so in order to make use of the information, we need to convert it to a different file format. The Windows Driver Kit contains a tool to do this.

  1. Download and install the Windows Driver Kit.


    The install may give warnings about additional software not being installed. These warnings can be ignored since we just need a standalone executable file from the installation.

  2. Run the following command:

    "%ProgramFiles(x86)%\Windows Kits\10\Tools\x86\Bluetooth\BETLParse\btetlparse.exe" c:\bth_hci.etl

    This will create a file with the same file name and a .cfa file extension (and an empty .txt file for some reason).

  3. Download and install Wireshark.

  4. Open the .cfa file in Wireshark to view the captured Bluetooth traffic.


On macOS, special software is required to capture and view Bluetooth traffic. You will need to sign up for an Apple Developer account to obtain this software.

  1. Go to and download Additional Tools for Xcode … where … is the Xcode version corresponding to your macOS version (e.g. 12 for Big Sur, 11 for Mojave, etc.).
  2. Open the disk image and in the Hardware folder, double-click the to run it.
  3. Click the Clear button in the toolbar to clear the old data.
  4. Run your Python script to reproduce the problem.
  5. Click the Stop button in the toolbar to stop the capture.


The Bluetooth traffic can be viewed in the or it can be saved to a file and viewed in Wireshark.


On Linux, Wireshark can be used to capture and view Bluetooth traffic.

  1. Install Wireshark. Most distributions include a wireshark package. For example, on Debian/Ubuntu based distributions:

    sudo apt update && sudo apt install wireshark
  2. Start Wireshark and select your Bluetooth adapter, then start a capture.


    Visit the Wireshark Wiki for help with configuring permissions and making sure proper drivers are installed.

  3. Run your Python script to reproduce the problem.

  4. Click the stop button in Wireshark to stop the capture.

Handling OS Caching of BLE Device Services

If you develop your own BLE peripherals, and frequently change services, characteristics and/or descriptors, then Bleak might report outdated versions of your peripheral’s services due to OS level caching. The caching is done to speed up the connections with peripherals where services do not change and is enabled by default on most operating systems and thus also in Bleak.

There are ways to avoid this on different backends though, and if you experience these kinds of problems, the steps below might help you to circumvent the caches.

Windows 10

The Windows .NET backend has the most straightforward means of handling the os caches. When creating a BleakClient, one can use the keyword argument use_cached:

async with BleakClient(address, use_cached=False) as client:
    print(f"Connected: {client.is_connected}")
    // Do whatever it is you want to do.

The keyword argument is also present in the bleak.backends.client.BleakClient.connect() method to use if you don’t want to use the async context manager:

client = BleakClient(address)
await client.connect(use_cached=True)
print(f"Connected: {client.is_connected}")
// Do whatever it is you want to do.
await client.disconnect()


The OS level caching handling on macOS has not been explored yet.


When you change the structure of services/characteristics on a device, you have to remove the device from BlueZ so that it will read everything again. Otherwise BlueZ gives the cached values from the first time the device was connected. You can use the bluetoothctl command line tool to do this:

bluetoothctl -- remove [mac_address]