I have the same car. The alarm should only go off if you have something relativly heavy on the seat. When I have to put things on the seat I connect the seat belt first then I put whatever object(s) on the seat. Edit: I think if you want to permanently disarm the alarm you will have to take the car in to a Toyota dealership.

I took my corolla into the dealership and they told me they would not tell me how to disconnect the alert for "safety reasons" which is a load of crap!

Here is your solution to the annoying seatbelt alarm (works on all Toyotas, I used it on my 2005 Corolla and yes, I always use my seatbelt): (1) Turn the Car "ON," but do not start the engine (leave your foot off the brake, don't fasten seatbelt). Cycle your trip reset knob until it reads ODO. Turn the ignition back off. Wait a couple of seconds. (2) Make sure your seat belt is not fastened. (3) Turn the ignition back on, do not start the car (leave your foot off the brake, don't fasten seat belt). As soon as you see everything light up, press and hold the trip reset knob and do a long 12 second count. (4) Keep your finger on the trip reset knob. Fasten your seat belt. As soon as you fasten your seat belt, you should see the ODO display go from XXXX miles to "b-on." At that time, take your finger off the trip reset knob and it should cycle to "b-off." If it doesn't, just press the knob again until "b-off" appears. Once "b-off" appears, turn the ignition off and unfasten your seat belt. Now, when you start your car, you should hear the "normal" seatbelt beeping, then when you go over 10 mph, if your seatbelt is not fastened, it won't beep 54 times... the seatbelt signal will just continue to flash... but no more annoying beep!!