https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1639-2014.pdf
Do they work or don’t they, I have seen my share of ones that had bugs or feces on them. Read this article from the University of Arizona and you make up your own mind.
There is some work on new devices and techniques according to the article, so stay tuned to a more in-depth probe into the mystery devices.