I suspected I had cat fleas in my house, and by the time I was sure it was too late. I have one cat, and a very clean house, but the fleas were a nightmare to get rid of. I tried Bob Martins Spot On on the cat and flea powder and sprays around the house, but to no avail. They would seem to be gone for a few days then appear again. This went on for months and was extremely frustrating.
I finally solved it by putting Frontline on the cat, and spraying the whole house with Indorex spray, concentrating on the edges of the rooms. The spray is the only one I found that seems to do what it claims and kill any unhatched fleas in the carpet.
Since then I have put Frontline on the cat as often as recommended on the pack, and they haven't come back. I have Indorex in the cupboard just incase!