I have used exactly what you're looking for. I don't remember the name. You put a metal jig on the carpet. The jig has three legs around a central hole. This lets you screw in special screws to a set depth. The screws are made with a weakening notch. After you screwed through the subfloor into the joist, you snap off the screw even with the subfloor. The tricky part is actually hitting the joist through the carpet.

I have the box packed away. I may be able to dig it out in the next couple days so check back occasionally.

david_wv, that sounds like a neat tool. If you think of the name of it, please post it.
Whenever I replace carpet, I go around and screw down the floor (even if it doesn't squeak now) while the old carpet is removed and the new is not yet down. It can get rid of current squeaks and save having new squeaks in the future.

Here's the product I have. I'm not saying it's the cheapest, priciest, best or worst. I don't even know if it's the only one or even for sale anymore. I do know it works. I ordered it out of a catalog but the box says:

Squeeeeek No More (I didn't name it)
O'Berry Enterprises
664 Exmoor Ct
Crystal Lake, IL 60014
800-459-8428