It creates random vibrations at the botton of the burried tube. 
You do need to install in on an angle, not straight up and down. There is clear instructions on the pack. 

Snakes see these vibrations as a threat and move away from the source. The vibrations travel about 20-30m through the ground.

We are prepared to guarantee these units to work. If you find you are still getting snakes once you  have installed in correctly and have active batteries in it, we will happily give your money back.
But I dont think you will be because these ones actually work.

FAQ’s