I generally use a "crystal" call with wooden striker. Its probably a poly carbonate material. Rub a little sandpaper on call to rough it up as the friction is what creates the sound.
Links are for the Kaput (warfarin based poison).
https://kaputproducts.com/feralhogs/
Special feeder information
https://kaputproducts.com/wp-content/uploads/2024/02/Kaput-Bifold-2023-Hog-4pg.pdf
I read up on it a LOT. I understand it is much safer for other mammals. The lethal dose for swine is very low in comparison to other mammals. Feeders designed to prevent consumption from animals other than pigs are available if not required for other poisons.