THE FIRST STEP IN DETERMINING THE EFFECTIVENESS OF A DETECTION MECHANISM IS TO BREAK THE MECHANISM INTO ITS FUNCTIONAL ELEMENTS. FOR IDENTITY/ACCESS AUTHORIZATION (I/AA) SYSTEMS, THIS BREAKDOWN IS IN THE FORM OF A CLOSED LOOP STARTING WITH THE FIELD OF VIEW AND ENDING WITH THE PORTAL CONTROL DEVICE, USUALLY SOME FORM OF REMOTELY OPERATED DOOR STRIKE. SUCH A BREAKDOWN OF FUNCTIONAL ELEMENTS IS DEPICTED. EACH INDIVIDUAL ELEMENT IS THEN TESTED TO DETERMINE IF TAMPERING OR COMPLETE CIRCUMVENTION IS CREDIBLE (THE TACTICS FOR DEFEATING EACH FUNCTIONAL ELEMENT OF THE I/AA MECHANISM ARE LISTED). THIS VULNERABILITY ANALYSIS STEP, A KEY FACTOR IN THE OPERATION OF MOST I/AA SYSTEMS, IS QUALITATIVE, AND THE RESULT IS TO SET THE DETECTION PROBABILITY EQUAL TO ZERO IF A VULNERABILITY IS DISCOVERED. IF NO CLEAR VULNERABILITY EXISTS, A PROBABILITY ANALYSIS SHOULD BE PERFORMED. IF THE SYSTEM IS WELL-CHARACTERIZED MATHEMATICALLY, IT CAN BE MODELED AND THE DETECTION PROBABILITY CALCULATED. IF THE SYSTEM IS NOT WELL-CHARACTERIZED, IT CAN BE STUDIED EXPERIMENTALLY, AND THE DETECTION PROBABILITY CAN BE MEASURED. AS A FURTHER TEST OF THIS PROCEDURAL FRAMEWORK, THREE OTHER DETECTION MECHANISMS ARE EVALUATED: A (SPECIAL NUCLEAR MATERIAL) PORTAL MONITOR, AN INTERNAL INTRUSION DEVICE, AND A MATERIAL BALANCE ACCOUNTING SYSTEM. IN ALL THREE EXAMPLES, MODELING THE MECHANISMS AIDED THE PREPARATION OF A LIST OF TACTICS TO EXPLOIT VULNERABILITIES. TABLES AND REFERENCES ARE INCLUDED. (WJR)