Brain Fingerprinting is a technique that uses EEG to detect brain responses called P300/MERMERs that indicate when a person recognizes previously known information. A sequence of target, irrelevant, and probe stimuli are presented while monitoring brainwaves. If probe responses match targets, it suggests the information is known; if they match irrelevants, it's unknown. Results have shown this technique can determine if information is present or absent in the brain in 90% of cases, always accurately. It has potential applications in advertising, counterterrorism, and criminal investigations.