Holy shit, it's the spike trap from every video game ever. :S
We use the same kind of traps in some cities in Denmark, and I think it was invented by a Dane as well. They are incredibly effective at preventing the rats in the edges of the network, but sadly they do nothing for the main sewer lines. We need AI and lasers for that, but that is far in the future.
The main benefit is that you know how many rats it have killed. And once there isn't more rats you can move it to a new place. You can get it for sewer lines from 110mm to 250mm I believe, so fine for the sewage lines that go into your property. In fact it's a cheap investment to guarantee that rats cannot enter your property through the sewers.
Sensors detect the rat and kills it immediately. Then it’s flushed out with other sewage. It also keeps count of how many rats are killed, which gives the city some numbers to use in their estimations.