Well, a conscientious and kind reader remembered that wish and sent me a link to ThermoWorks' EcoTemp Alarm Thermometer.
At $39, I felt it was an affordable convenience for something I intend to use consistently and often. I added a few accessories... a clip so it can hold onto the sides of pans and bowls, a protective cover, and an additional probe that allow it to be used in my probeless bottom oven. So my overall price was about $65. I've used it SO many times in the several weeks I've had it, and I just finally used it to make yogurt again this past week.
In making yogurt (using the same recipe and methods as the first time), it's the first time I've tried setting the alarm or using the clip.
Either I'm not setting it up right, or the clip is a bit flimsy and awkward, but it does the job.
The alarms, though, were WONDERFUL. There weren't any directions for using it, but I found setting it to be pretty easy to figure out. 
I set the high temp for 200 as the milk warmed slowly, on a medium-low flame. Heating the milk not only allows it to ferment in a reasonable amount of time, but taking it past 185 will denature the proteins and it will be thicker.
When the milk was transferred to a bowl to cool, I set the alarm for 112, so I had time to get there and cover the bowl for transfer to the oven, without it getting cooler than the 110 degree fermenting temperature.
Then, as before, it went into the oven, set on Proof at 110 degrees, and stayed there for hours. Since I used a gallon of milk and I didn't know if the quantity in the bowl needed more time, I left it to ferment for about 8 hours this time, before carefully transferring it to the fridge for an overnight sit... instead of 4 to 5 hours in the oven like last time.
I think that made it a little more sour, and I won't leave it that long next time. But there will definitely be a next time, because this thermometer made the job easier and more certain.
