Do you use “a” or “an” before acronyms?
Take "StackExchange" and its acronym, SE, as an example: I read a StackExchange thread the other day about the history of bananas!
If you were to use the "SE" acronym instead of "StackExchange," you would probably write: *I read an SE thread the other day about the history of bananas!* The way in which this differs from my situation is that it's very reasonable to assume that when you write "SE," that you are perfectly fine with the two letters "ess" and "eee" standing in for "Stack Exchange," much like FCC, SEC, NASDAQ, NATO, etc. completely stand in and are even far more well-known than their longer, official names.
Let's say, however, that you're talking about "solar-powered asynchronous communication transmission," which you abbreviate with "SPACT" because you don't want to keep retyping "solar-powered asynchronous communication transmission," not only because you want to be lazy but also because reading those words more than one time every sentence can get in the way of comprehension. Now, if you were to pronounce this "ess-pee...etc." then, of course, you'd say "an SPACT device," but let's say you don't want "SPACT" to be referred to, phonetically, by its letters (or even "SPACT") and are simply using it as an abbreviation? Does it retain its indefinite article ("a") from its original version ("solar-powered asynchronous communication transmission")?