I use exclusively portable radios. Recently, I wanted to revisit my Degen DE321 to see how it tuned strong local signals and what kind of tuning refinements were possible. So I put a couple alkaline batteries in it and tuned to my usual local news radio station, KCBS AM 740.
At some point, I was ready to switch it off and do something else. I picked up the radio and thoughtlessly moved my thumb along the right side. I heard a click sound and thought "okay, it's off." But then I took another look at it, and saw the Tune light was still lit. Then I remembered that there was a power switch on the left, and what I did was probably lower the volume.
If the volume dial didn't end with a hard stop, I would've noticed my error right away. There's something that portable radios could adapt from smart phone user interfaces: an indication that the end has been reached. When scrolling to the edge of a page, there's a sort of rubber banding effect that lets the user continue to move the content but smartly indicates that the edge was reached. What if volume knobs and tuning knobs continued to travel a bit at the edges, and produced a quick vibrate?