Rat repellent isn’t the solution
Folklore says that strong smelling items such as moth balls, peppermint oil, bath salts, etc, will repel rats as they interfere with the rats incredibly sensitive olfactory senses – yes, perhaps, this may work in a very confined space, but, if you want to try and apply it to an entire building most likely the quantities required would push you out the house first long before the rats.
Likewise, there is discussion regarding cat urine and dog hair but there is also evidence to show these things can actually speed up reproductive rates in rats rather than suppress it. It may sound bizarre, but, when you think about it, it is actually the logical response to increased predator presence in your habitat.
Ultrasonics are probably the most well known repellent solution for rats, but, there couldn’t be a more useless strategy in our book. This is a system used by bats to fly through the dark without bumping into things, so don’t think some ultrasonic noise from a room somewhere is going to make its way through into a wall cavity.
There is also no real evidence to show that rats show any distress to ultrasonics. For the rats, it is probably a bit like living near to a railway line, noticeable at first, but eventually it just becomes part of the day-to-day noise you get used to.
Needless to say, no professional supplier to the licensed pest control industry sells them, it is just just a gimmick, but at an attractive price point to consumers so they still sell well.
Don’t try to repel rats – fix the point of entry
In reality, believe it or not, the best repellent for rats would be other rats, as these animals are typically strongly territorial and competitive over resources. However, introducing rats to get rid of rats obviously confuses the overall objective somewhat.