Forget pepper spray. It's not wise to use it indoors, because you're very likely to absorb a debilitating amount of the spray yourself. It's also fairly common for it to blow back on you when you're outdoors.
Get pepper gel instead. The gel is safe to use inside and out, with very little chance of blow back and self-contamination. Pepper gel also has better range than spray or foam, with an effective distance usually around 18 feet.
Pepper gel is also more effective at stopping aggressors, due to the fact that it sticks to their eyes, nose and mouth like glue. Nasty stuff that's virtually impossible to wipe away without making things worse.
I recommend 10% OC with UV dye. I use MACE brand, but there are several companies out there that make a quality product.