Monitoring mode allows you to observe all CEC messages being sent on your HDMI network in real time. This is useful for diagnosing why a CEC command is not working, checking what commands your TV or devices are sending, and debugging integrations with media centre software or home automation.
Requirement: You must have libcec installed first. See: How to install libcec (Windows)
Running Monitoring Mode on Windows
1
Open a Command Prompt — press Windows + R, type
cmd, and press Enter.2
Navigate to the libcec installation folder:
cd "C:\Program Files\Pulse-Eight\USB-CEC Adapter"If this path does not exist, try:
cd "C:\Program Files (x86)\Pulse-Eight\USB-CEC Adapter"
3
Start monitoring mode:
cec-client -m
4
CEC messages will appear in the Command Prompt window in real time. Press Ctrl+C to stop.
Understanding the Output
Each line of output represents a CEC message, for example:
TRAFFIC: [ 15:45:22.417] >> 0f:36
The numbers after >> are the raw CEC command in hexadecimal. You do not need to decode these to use monitoring mode for basic troubleshooting. The key things to look for are:
- Are any messages appearing at all? If nothing appears when you press buttons on your TV remote, CEC may not be enabled on your TV. Check your TV's settings for a CEC option (Anynet+, SimpLink, Bravia Sync, etc.) and ensure it is turned on.
- Is the adapter detected? If cec-client reports no adapter found on startup, check the USB connection and that libcec is correctly installed.
Running Monitoring Mode on Linux / Raspberry Pi
On Linux or Raspberry Pi with libcec installed, run the same command from a terminal:
cec-client -m
If you have multiple CEC adapters available, specify the adapter:
cec-client -m /dev/ttyACM0
All cec-client Options
To see all available options for cec-client, run:
cec-client -h
