<p>Counterfeiting of metal alloys poses a significant challenge in industries including aerospace, automotive, construction and electronics, where material integrity is critical. The infiltration of counterfeit alloys can lead to severe consequences such as product failures, safety hazards, financial losses, and damage to the reputation of legitimate manufacturers. To address this growing concern, various authentication technologies are currently employed to detect and prevent the circulation of counterfeit metals/alloys. This study introduces an innovative solution to counter the escalating threat of counterfeit metal alloys, by integrating an upconversion phosphor into a tin-lead alloy, offering a built-in, dual-layered anti-counterfeiting system. This system features both visual and auditory authentication mechanisms without compromising the alloy's functional performance. When exposed to a 980 nm light source, the material exhibits a distinctive distance-dependent multi-colour emission pattern; a vivid red glow at close range, shifting to orange at an intermediate distance, and reverting to red when viewed from farther away. In addition to visual identification, the modified alloy incorporates an additional layer of auditory authentication feature; emits a beep sound when scanned with an infrared taggant detector. Unlike conventional methods that rely on external security measures, this novel approach embeds multi-level anti-counterfeiting features directly within the alloy, enhancing security and resistance to tampering.</p> Graphical Abstract <p></p>