From subaruoutback.org (search disable seat bet chime subaru):
"1. Turn engine on (may work in ACC, but definitely when on).
2. Within 30 secs of ignition
, clip/unclip seatbelt 20 times.
That's it, no on/off cycles to do. This worked first time for my car - 05 OBXT. Setting will last until the microprocessor is reset or battery disconnected.
For a temp disable of chime, do the clip/unclip cycle 3 times only, will reset once ignition is turned off again. Handy for the disgruntled passenger who refuses to buckle up."
If you disconnect your battery you will have to do this again. There is also a way to permanently disable the chime: http://www.subaruoutback.org/forums/...e-removal.html
Hope this helps.