I have one as above, it's stays green above 12volts, so by the time you get to yellow, ouch. Oh and in bright 100F temps you can only easily see red, yellow is dim, green invisible.
the one JR has linked to has more granularity about voltages.
Personally, I'm going to get another one of these...
I used one for years on my GSPD, I trust it. It doesn't work when wet or real cold, but wakes up as the day dries out and warms.
RANT on........Why couldn't they have added a voltmeter function to the trip computer, or somewhere? Especially considering they used to do it for airheads, which didn't have a digital voltage cutoff point, just lousy electrics, but would run and drive safely with low voltages. Now we have slightly more modern electrics which are 100% dependent on proper voltages and we can't keep an eye on that. It's almost like providing no way to determine gasoline level, "oh just drive till it quits and call customer service". rant off