Free coin tester

Yes. Every test with the browser coin tester is free, with no limit and no sign-up. The Pingcoin app for iPhone and Android includes 15 (iPhone) or 10 (Android) free tests a month, with paid plans for more.

A coin rings at frequencies set by its metal, size and shape. The tester listens to that ring through your microphone and checks whether its three main resonance frequencies fall where a genuine coin of that type rings. A fake made of a different metal, or with a different weight or thickness, rings at different frequencies.

A phone, tablet or computer with a microphone, the coin, and something hard to tap it with, such as another coin or a pen. Hold the coin lightly at its center, pinched or balanced on a fingertip, so it can ring freely, then tap its edge near the microphone.

Not necessarily. A noisy room, holding the coin by its rim, or a tap that was too soft can all hide a frequency. Try again somewhere quiet, holding the coin lightly at its center. If it still does not match, check its weight and dimensions too before you draw a conclusion, and treat a ping test as one check among several.

No. Your browser listens for a tap and sends only the fifth of a second of sound after it to our server, which checks the ring and doesn't keep the sound. We keep the outcome of each test (the coin, the verdict and the frequencies heard, with a random id for this browser) to improve the reference values for every coin.

They use the same idea: compare the ring with known reference values. The app is built for testing on the go, at a coin show, a dealer or an estate sale. It works offline and keeps the coin library on your phone.