I love this amazing ceramic amplifier designed by Science and Sons...
Below a “how it works” explanation taken from their website:

“Without the use of external power or batteries, the Phonofone inventively exploits the virtues of horn acoustics to boost the audio output of standard earphones to up to 55 decibles* (or roughly the maximum volume of laptop speakers). Upon connecting active earphones to the Phonofone their trebly buzzing is instantly and profoundly transformed into a warm, rich and resonant sound.”

“The Phonofone is constructed entirely from ceramic. Not only environmentally low impact, ceramics are inherently rigid and resonant, lending themselves well to this application.”