It was on the garage wall, I also have one in my garage.
door bell transformer, what do i win 
remove one wire and try your doorbell
Yup, Barry wins!
With a flush mount panel it is hard to find a way to legally bury one of those suckers. That is why you sometimes see them illegally laying inside some electrical panels. :mad:
Around here you usually find them in the attic above the doorbell location.
Test it as you would a 9 volt battery, use your tongue! 
When you see two of them, one is for the alarm system.
Not necessarily. The NuTone intercom systems take two.
If you find these transformers in the attic, you’ve also found a hazard.
Yeah, I know…but it doesn’t stop them from putting them up there. Kinda like the ground rod clamps we find most of the time are not approved for that particular application either.
Why is that so?
Does this help?
They say specifically on the package not to install them in attics. I assume it has something to do with the tamp rating of the transformer itself.
So, if you are asked, what do you suggest as the optimum way to install such an item?