It's not the first acoustic soundhole tuner we've seen - that would be Korg's Rimpitch - but D'Addario's Micro Soundhole Tuner is certainly the smallest and least intrusive.
Mounted via a non-marring universal mounting clip, the tiny chromatic tuner is concealed within your guitar's soundhole.
A highly sensitive piezo transducer detects vibrations from the soundboard, promising fast and accurate tuning response, while the bright display makes for easy viewing.
The NS Micro Soundhole Tuner is designed for acoustic guitars, basses and ukuleles, and offers an A435-455 calibration range. It's available now for £19.90.