There are tuners that only recognize certain tones, for example only 6 strings of the guitar. While chromatic tuners recognize all 12 semitones over several octaves. The currently most common variant of tuners are the "clip-on" tuners. These are small devices which are clamped on the head of the guitar, for example. The tuner recognizes the tone directly from the structure-borne sound. The big advantage: the tuner precisely sets the tone; environmental noise is not included. The standard models are based on a built-in loudspeaker. These larger models sometimes offer more setting options or different special moods, such as 'Flat-Tuning'. Tuners are also available as pedals. These can be switched directly between guitar amp and guitar.