No doubt, this is a special category. Effectively, I want a tactical flashlight in my jean's key pocket.
Here is my Top Pick for Best Key Pocket Carry Tactical Light
By tactical flashlight, I mean one button accessibility, either tail or side control, for permanent high and strobe with a lumen rating of more than 250.
A full-featured tactical light would also offer momentary, which my recommendation does not, however, for the size, you're getting an awful lot and its size, with the ability to consistently carry, in my mind, offsets the deficiency of not having a momentary.
There are other lights that I would recommend for gun carry tactical lights but they are larger. This is the type of light I would recommend for self-defense and that would be constantly available to anyone.
Always be prepared, be well.