I didn't know it had a siren. I just tried it on mine and yes it has a siren. Must have come through a recent update. It can be disabled with the power button on mine without needing to turn it off. Just try holding the power button for 1-2 seconds instead of the 3-4 seconds that shuts it down.
MWR Price at posting:
$3.30 Sentiment: Buy Disclosure: Held