If you're going with sprays though, you might as well go with true OC. It's respected by LEOs and courts for its defensive uses, it's water soluble if you get it in your car, it's not permanently damaging if you accidentally hit yourself with it (unlike wasp spray or flares). You burn yourself with a flare or get wasp spray in your eyes, you could be permanently disfigured or disabled. At least OC washes out after a day or two with no lasting effects. Get was spray in your eyes and you might be walking with a seeing eye dog for the rest of your life. OC is safe, non-toxic, doesn't destroy your car or hurt yourself, and has UV marking to identify your attacker later on.
If you're really thinking about keeping some non-firearm defensive tool in your car door, just go with something that is already well established as a less than lethal option. OC and maybe a baton if you are allowed and know how to use it. Keep the flares in the trunk and the wasp spray in the garage.