I’ve seen a battery program that would draw a bar on the top edge of screen as the battery life indicator. I was thinking if we could have a 1-by-1-pixel red dot on top-right corner like the HDD activity LED.

Of course, as usual, I lost interest, but I do have a working script. Just note that it doesn’t paint a red dot, but simply shows the indication in terminal, here is the script:

#!/bin/bash
# Written by Yu-Jie Lin
# Public Domain

DISKSTATS=/proc/diskstats

while sleep .125; do
  current="$(<$DISKSTATS)"
  if [[ $current != $last ]]; then
    xset led
    echo -ne '\e[2D\e[1;41m  \e[0m'
    last="$current"
  else
    xset -led
    echo -ne '\e[2D  '
  fi
done

I got the idea from this code, I didn’t port the code, just stealing the idea of its comments. It’s much simpler when you only check entire content of /proc/diskstats is changed.

Also, it uses the Scroll Lock LED via xset command, didn’t know you can control the LEDs until I found this answer. Now come to think about that LED, it finally has a purpose, I don’t even know how to use the Scroll Lock.