I know I've mentioned this before on this forum to others, but I can't stress it enough: If you see ants, get a monthly pest control service. Rentokil costs $900-$1,000 per year, but I don't know if they've changed rates in the past year (and there are other companies as well). Definitely worth the cost, in my opinion.
Over-the-counter products might work for a day or two but the ants will be back. Even if you live on a high floor in a nice, new
condo and keep it clean, there's a good chance you'll still see ants. Where there's one, there are more. You kill one yourself, an army will show up within seconds.