2003 Hummer H2 Security indicator light

Hello .. thanks for the donation .. much appreciated

The Alarm/immoboliser on you vehicle is controlled by the vehicles on board computer and will need to be read by a diagnostic scanner to locate the cause of the fault i'm afraid ..

VEHICLE THEFT DETERRENT (VTD) DESCRIPTION & OPERATION
Passlockà † System
The theft deterrent system has been incorporated into the body control module (BCM). The theft deterrent is provided in order to prevent the vehicle operation if the correct key is not used in order to start the vehicle. The ignition key turns the lock cylinder. The cylinder rotation produces an analog voltage code in the Passlockà † sensor. This voltage code is received by the BCM. The BCM compares the voltage code to the previously learned voltage code. If the codes match, a class 2 message is sent from the BCM to the powertrain control module (PCM)/vehicle control module (VCM). The message enables the fuel injectors.
The design of the Passlockà † system is to prevent vehicle theft by disabling the engine unless the ignition lock cylinder rotates properly by engaging the correct ignition key. The system is similar in concept to the PASS-Keyà † system. However, the Passlockà † system eliminates the need for a key mounted resistor pellet. The components of the Passlockà † system are as follows:
The ignition lock cylinder
The ignition switch
The Passlockà † sensor
The Body control module (BCM)
The security telltale
The vehicle/powertrain control module (VCM/PCM)

DIAGNOSTIC STARTING POINT - THEFT DETERRENT
Begin the system diagnosis with the Diagnostic System Check - Theft Deterrent. The Diagnostic System Check will provide the following information:
The identification of the control module(s) which command the system
The ability of the control module(s) to communicate through the serial data circuit
The identification of any stored diagnostic trouble codes (DTCs) and their status
The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

hope this helps .. let me know