A click for every wheel step and press, like the real iPod's. On iPhone the click plays even with the silent switch on (Safari 16.4+).
Each button flips the line the firmware watches and shows its level. Power alone is a charger. A cable makes the iPod ask to reboot into disk mode. The battery line reads low from power-on, but the firmware only reacts to an edge: set it high, then low again, and it draws "Low Battery".