Voici le script qui a résolu le problème
Laptop headphone detection in Karmic solution
It seems that with the new Karmic there is no obvious way to enable headphone detection. After a bit of googling and some testing it turns out that all you need to do(at least on my laptop) is to "unmute"(funny term) Alsa's 'Headphone Jack Sense'. In previous Ubuntu versions you could enable it right in the volume control, but Karmic requires a little more work.
A big thanks to egaistek at vaioubuntu whose post got me looking at amixer.
The quickest way of doing it is to run alsamixer in a terminal and unmute 'Headphone Jack Sense'. Navigate to the control and press 'm'. If it in the top left corner before said Item: ...... 'off', 'off' should now be gone. Exit with Ctrl-C. Done!
The more practical way is to use amixer and make a script that is run every time you log in.
In the following steps, replace the X in /home/X/headphonejs with your user name.
Create the script. Open gedit Text Editor(Applications->Accessories->gedit) and paste in the following:
# Script for activating Headphone Jack Sense
#Andreas Wileur <firstname.lastname@example.org
amixer -c 0 sset 'Headphone Jack Sense' unmute
Save the file in your home directory, call it headphonejs
Make it executable. Press ALT+F2 to open the run dialog. Enter the following and press enter:
chmod +x /home/X/headphonejs
Make it run at startup Go to System->Preferences->Startup Applications.
Click 'Add' and enter the following:
Name: Headphone Jack Sense
Comment: Activate Headphone Jack Sense
Click 'Add' and then in the first window 'Close'
Start it. Now you can either logout and re-login or manually run your script by pressing ALT+F2 and entering this: