Thanks to my.is Senior Moderator METEORO who brought this tutorial over from Club Lexus.
Seat belt chime On/Off
Someone posted the steps on how to disable the chime over at CL...
Just did it...works.
Here are the steps:
1. turn the key to the ON position which means pressing the start button twice on the new IS since it doesn't has the key, foot off the brake
2. Press the trip reset button couple of times until the ODO is displayed (not trip A or B)
3. turn the ignition to the LOCK (OFF) position
4. unbuckle the driver's seatbelt if it was buckled.
5. turn the key to the ON position again press the start button twice. when the dash lights comes on, press and hold the trip reset button and count a slow 12 seconds. (editor's note, hold it more like 30 sec)
6. while still holding the trip reset button, buckle the driver's side seatbelt.
7.and the odometer display should read "b ON" or "b OFF". toggle the beep OFF with the trip reset.
8. the process should be completed when you unbuckle or turn the key off.