AT-01B Keychain Style Digital Chromatic Tuner for All Instruments. Chromatic Tuner with Keychain attachment. Carry it with you always. Internal microphone picks up the sound from your guitar, sax, violin or other instrument. LED backlit display shows arrows for Sharp/Flat and changes from Orange to Green when you are in tune Pitch Accuracy +/- 0.5 Cent. Pitched to A=440Hz CR2032 Battery Included