Outside, dh has sprayed near the foundation during the summer, when the ants seek entrance to escape the heat. We don't like to use toxic sprays, as they enter the environment (I know you know this) . . .
We've used an ecologically-safe spray inside the house (we have cats and kids), only where the ants are entering (I search down the entry point, usually the kitchen, around the windows, and spray there). Then I clean up all the ants I can find. Doesn't help, that our house is built where an orange orchard once resided (resode?????

).
The stuff smells weird, but it'll dissipate in a day or so . . . The brand is "Bioganic," "crawling insect killer," touts itself to be "safe around children and pets," and is sold in the grocery store (has endorsements of Good Housekeeping and Jane Seymour on the can

).
Recently we had the beginnings of an ant invasion, and no matter how much I search and searched, I could NOT find the entry/source!!! Then I happened to jostle one of the plants in the kitchen and lo! The ants had made a home inside the pot, in the dirt, and THAT was the source! That plant is now making its home OUTSIDE!!!
Good luck!!