There are a few myths that have circulated regarding using keys for self defence. (I keep mine on a flashlight, but that’s for another post.)
The main one I’ve heard is that you should position a key between each of your fingers so that, should you be accosted by a violent assailant, you could punch or swipe your fist into their face or other soft target.
The downsides are, first, that those keys will likely fold into your hand and cut you as badly as you were hoping to damage your attacker.
Secondly, whether you needed to deploy the “weapon” or not, you still need to organize the key that will get you through your car or house door to safety.
Consider holding the next key that you need firmly between your thumb and forefinger, ready to use in the next lock.
If you need it as a defensive tool, it will jab into an attackers face or other target more firmly and effectively than the three between your fingers.
The upside is that you will not need to search for the right key when you get to the locked door as you already have it ready.