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My laptop is Thinkpad Edge series, of which laptop will produce a beep when the power supply being unplugged. But I noticed that the beep has been blocked if the alsa is turned to mute.

So, I wonder if I can add an exception of "mute rules".

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2 Answers 2

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The wide variety of sound cards and ac adapters may make this difficult for a universal answer, but the basics are:

  • Create a daemon process that monitors /proc/acpi/ac_adapter/state for "offline" (grep will do fine)
  • Use that to trigger setting volume to X (see alsactl --help) and playing a sound/beep (aplay, beep, ...)
  • Return sound to system setting (the alsa settings are in /etc/asound.state)

Note: if you don't have /proc/acpi/ac_adapter/state, use something else that would change when the cord is pulled ... like /proc/acpi/battery/BAT1/state (the charging state would become discharging)

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A good idea, but I have no ac_adapter in /proc/acpi directory. –  Determinant Mar 26 '12 at 8:55
    
I updated with an alternative file to monitor in /proc/acpi ... it would help if you gave a listing of /proc/acpi and more detailed info of your applicable hardware in general (hardinfo will work ). –  technosaurus Mar 27 '12 at 3:59
    
I'll have a try on it. The acpi of my laptop is poorly supported. Thank you anyway. –  Determinant Mar 27 '12 at 12:59

You can not. Alsa mutes using hardware mixer so well that not even a mouse whisper passes.

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Any other approach to my problem? Any other low-level solutions that can make sound using the device directly? –  Determinant Mar 20 '12 at 13:00
    
10 years ago there were speaker pins on all motherboards. now they are silently routed to a builtin soundcard. You may find connector en.wikipedia.org/wiki/PC_speaker#Pinouts or you need to solder one. remember that 4-pin connector is sometimes serial 12V and will burn headphones. –  ZaB Mar 20 '12 at 13:32
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Well..My computer is a laptop and I mean I need a software-level way to achieve that (maybe some kernel hacking on sound devices). –  Determinant Mar 20 '12 at 14:03
    
well snd-hda-intel file has it. replace master channel mute by mute of all but speaker.... –  ZaB Mar 21 '12 at 13:24
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Could you please give me some specific instructions? –  Determinant Mar 25 '12 at 15:13

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