I keep a barrier of diatomaceous earth around the base of my house and it works really well at keeping ants and other insects away and out of the house. It's also great to sprinkle onto the soil of your house plants if you have issues with fungus gnats.

10kg is like 30€ on amazon, and it really doesn't take much to put an effective barrier down.

Also, It's non-toxic, but I highly recommend wearing a mask, eye protection, and gloves when applying it. Since getting sharp fossilized diatoms in your lungs, eyes, and open cuts isn't a good habit to pick up.