I'll be eating my hat, then; this thing is indeed real,

https://carlwillis.wordpress.com/2017/02/07/analysis-of-sovi... ("Analysis of Soviet smoke detector plutonium" (2017))

(and HN thread, https://news.ycombinator.com/item?id=13616574 )

That analysis says these contained about 40 μCi of Pu-239, or 0.7 mg.