OK, if you want to fix those squeaks (this is for the teenagers), here’s how. If you can get under the stairs, just affix an “L” bracket to the stringer (then piece the stairs sits on) and the bottom of the treads themselves. Make sure not to drive a screw all the way through the stringer or the tread, otherwise you might end up with bloody stairs.
If you can’t get underneath the stairs, there are some commercially available kits or you can simply use a trim screw from above. There are also some small-headed screws available that you can punch right through the carpet without damaging it.