Odorless material which is both easy to apply and effective. Available in a liquid which is actually a micro encapsulated material or wettable powder. Either form will lay on concrete surfaces well providing long term residual and control.
Many pests are on the label but it works great for millipedes or centipedes.
Cyfluthrin will provide a quick knockdown coupled with a good residual and low toxicity. Outside on the foundation wall creating a wide band of treated surface to stop millipedes or centipedes from coming inside. You may need to spray the whole side of a building if the migration is severe. Also use it along the border of where mulch, turf and cement meet. Can be applied around plants and shrubs where nests are thought to be living.