Sennheiser Set 820 Instruction Manual page 29

Where to place the transmitter
Choose a suitable place near or on
top of your hi-fi system or TV set.
Do not place the transmitter close
to metal objects such as shelf bars,
reinforced concrete walls, etc.
The transmitter features a
convenient automatic on/off
function. The transmitter is
turned on by the audio signal.
If there is no audio signal for about 3 minutes, the transmitter automatically
turns off. The transmitter is now in stand-by mode, its power consumption is
very low so that it can remain connected to the mains. Batteries can always
be recharged when the transmitter is connected to the mains.
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