To anyone using GRJ's design as a starting point to learn the tool. Here's a project.
Only 1/2 of the 123 chip is being used. This means you can add a 2nd threshold and 2nd LED which might make the tool more useful. So LED1 would blink when a full level packet (12V or whatever you guys come up with) is detected. And LED2 would additionally blink if the packet is above, say, 50% of the full level. The component cost would be pennies - LED plus a few resistors, caps. Not as handy as having 4 thresholds but small steps.
With only one LED, if it doesn't blink it could alternatively mean that the battery is dead. 
Separately, if modifying the 1 LED design, I suggest terminating (e.g., tying to ground) the input pins on the unused half of the 123 chip. It is not a good idea leave unused inputs "floating" (not connected to anything).
