Small pointy hot peppers tend to be hotter than large round ones. The little ones are hotter because they have more ribs and seeds, which have more capsaicin.
Chili powder is made of ground mild and hot chiles, oregano, and cumin. Some kinds also contain garlic and salt.
If your chili powder is getting old and needs to be replaced, it doesn’t have to go to waste. Sprinkle it generously over bulbs when you plant them to keep the squirrels out of them, or on top of the soil to protect established bulbs.
By the way, if you like to feed your neighborhood squirrels, you can reduce the amount of digging they do by cracking the nuts you put out for them (and not putting out very many at a time). They bury nuts to soften the shell; if they can get into the nut right away (and aren’t full) they’ll go ahead and eat it.