Anyone who has read The Odyssey has “met” the original Sirens … the mythological creatures in Greek history who lure sailors to their destruction on rocks with their sweet singing. But I daresay most of us haven’t looked too closely at the word.
The Greek seirenes is from seira, which means “cord, rope.” The idea, then, is that these women bind or entangle their pray–with song, in the case of the Sirens. It’s interesting to note that in Greek, the same word was used metaphorically for any deceitful woman.
As English developed, they preserved the word as it appeared in Greek from the 14th century, keeping that metaphorical sense too.
So…what about the modern day sirens? As in, devices that make a loud noise? Those date from around 1879 and were first used on steamboats. Why that word? I couldn’t find written evidence of the reason, but my own reason suggests that it was a bit of linguistical irony. Sirens, which once were said to lure sailors to their death with a sweet song, will now warn people of danger with a loud, unpleasant noise.