A miniature surface-mount voltage divider for sensitive in-ear headphones. Without attenuation these devices can easily produce 130+ dBu SPL at full volume; loud enough to damage hearing in seconds.
Wiring this circuit into a pair of headphones (or an adapter) will reliably limit the maximum level produced.
It's tiny at 0.2 x 0.27 inches and mounts four 0805 (imperial) resistors, two per channel. The circuit below uses 20 ohms for R1,R4 and 0.2 ohms for R2,R3 which results in 40 dB of attenuation.