Most dealers and stackers point to the Sigma Metalytics Precious Metals Verifier as the top choice. It uses electromagnetic waves to measure the resistivity of the bulk metal, penetrating below the thin plating used on most counterfeit coins and bars.
It works in less than one second without affecting the coin or bullion, and can even test coins through plastic cases or slabs. Alternatives include XRF analyzers (more precise but costlier) and simple tools like ping testers, digital calipers, and precision scales for basic checks.
For most collectors and stackers, Sigma Metalytics offers the best balance of accuracy, speed, and affordability, though pairing it with weight and dimension checks adds extra confidence.