2003 GMC Sierra 1500 Pickup Owner's Manual - Page 106

If a door is opened without the key or the remote keyless entry transmitter, the alarm will go off. Your vehicle's headlamps will flash and the horn will sound for about two minutes, then will turn off to save the battery power. Remember, the theft-deterrent system won't activate it you lock the doors with a key or use the manual door lock. It activates only if you use a power door lock switch with the door open, or with the remote keyless entry transmitter. You should also remember that you can start your vehicle with the correct ignition key if the alarm has been set off. Here's how to avoid setting off the alarm by accident: If you don't want to activate the theft-deterrent system, the vehicle should be locked with the door key after the doors are closed. Testing the Alarm The alarm can be tested by following these steps: 1. From inside the vehicle, lower the driver's window and open the driver's door. 2. Activate the system by locking the doors with the power door lock switch while the door is open, or with the remote keyless entry transmitter. 3. Get out of the vehicle, close the door and wait for the security light to go out. 4. Then reach in through the window, unlock the door with the manual door lock and open the door. This should set off the alarm. If the alarm does not sound when it should but the vehicle's headlamps flash, check to see if the horn works. The horn fuse may be blown. To replace the fuse, see Fuses and Circuit Breakers on page 5-1 71. Always unlock a door with a key, or use the remote keyless entry transmitter. Unlocking a door any other way will set off the alarm if the system has been armed. If you setoff the alarm by accident, unlock any door with the key. You can also turn off the alarm by pressing UNLOCK on the remote keyless entry transmitter or by placing the key the ignition and turning it to START. in If the alarm does not sound or the vehicle's headlamps do not flash, the vehicle should be serviced by an authorized service center. 2-19