SKL Electronic 3 in 1 LCD Clip-On Guitar Tuner Metronome Tone Generator 3 in 1 function:it is not only a tuner,but also a metronome,tone generator Backlight and LED indicator making the tuner easy to use in dark situation It is not only a music instrument tuner,but also a good tool for vocalization practice. Automatically power off if no signal is received in 3 minutes. Power supply:2 x AAA batteries (not included)