An anemone is a “moan” made by someone suffering from anhedonia when he or she achieves an orgasm. Anhedonia is the inability to experience pleasure. Consequently an anemone is typically barely audible.
Because they are so quiet, if you are enough of a pervert that you want to detect when someone is “moaning” an anemone you need a highly sensitive audio detection device known as an anemometer to do so. There is not a lot of call for anemones because, really, if you’re into that sort of thing wouldn’t you rather watch porn starring people who at least appear to be enjoying themselves?