Sennheiser M3AEBTXL Instruction Manual page 16

Make sure that Bluetooth is already activated on your Bluetooth
device when switching on the headphones.
If Bluetooth is activated and the headphones cannot find a
paired Bluetooth device within a few minutes, you hear the
voice prompt "No device found". The LED lights up red for
2 seconds. The headphones switch to standby mode.
Unfolding the ear cups without switching the headphones on
▷
Press the multi-function button while unfolding the ear cups and hold the button for at least 4
seconds.
The headphones remain switched off. You hear the voice prompts "Power off". The LED lights up
red for 2 seconds.
To switch the headphones on again:
▷
Fold both ear cups inwards and unfold them again.
The headphones switch on normally (> 16).
Switching the headphones on without Bluetooth wireless connection
(flight mode)
▷
Press the voice assistant button while unfolding the ear cups and hold the button for at least 4
seconds.
The headphones switch on without Bluetooth wireless connection. You hear the voice prompts
"Power on" and "No connection". The LED lights up green for 2 seconds and then red for 2 seconds.
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