For anyone considering purchasing these sirens, note that there are 2 versions that look identical.
The one referenced here is the "cheaper" version (usually <$20USD) it DOES NOT have a temperature or humidity sensor that is present in the more expensive versions. They are USB powered with battery backup. The vendors play fast and loose with their descriptions so read carefully if you want the temp & humidity feature.
It functions as a ZigBee router. I haven't tested it for long term stability as a router though .
This is what they look like.
