I found this post via genvibe.com, it worked for me on my 07 Vibe:
This will turn off the 1 minute beep if the car is running and either the passenger or the driver takes off their seat belt. Get in the car and turn the key to on (don't start the car,) then change the odometer to display "odo" and not trip A or B. Turn the key off. Turn the key back to on. Within six seconds of doing this, press and hold the odometer button. Do so for 10 seconds. Then, while still holding the button, buckle up, edit: then unbuckle. The "odo" display should then change to say "b-on." let go of the odo button to get it to read "b-off." Then wait for the display to change back to the odometer. That's it, you're done. The car will still beep right when you turn it on for 3 seconds if you don't have a seatbelt, but the dash light will continue flashing till buckled up. It won't beep if you or your passenger unbuckles for a moment. Salvation!
To disable the seat belt alarm on a Chevy Colorado, locate the alarm fuse. Pull out the fuse to disable the alarm.
How do I disable seat belt alarm for a Ford F150 2004
Wear the seat Belt !
I find that fastening the seat belt disables the alarm immediately
The easiest way is to use the seat belt. There is also a method to described in http://forums.genvibe.com/zerothread?id=18678 for 2005-2007 models
You wear your seatbelt!
Buckle up!
Buckle up.
take out the fuse for it
By wearing your seat belt.
To disable the seat belt alarm in a Chevy Trailblazer, you typically need to buckle and unbuckle the seat belt multiple times in succession. Start by buckling the seat belt, then unbuckle it and repeat this process about three times within a short timeframe. After doing this, the alarm should be disabled. However, it's important to note that disabling the seat belt alarm may not be recommended for safety reasons.
You must fasten your seatbelt