Based on my experience, the S&W 642 is one of the best choices for concealed carry. Its weight and dimensions allow many to carry it in a pants pocket (a pocket holster is recommended). I prefer a belt holster or jacket pocket. It is rated for +P ammo, so it does represent a reasonable power level for self-defense. It will take some practice to be comfortable shooting it with any degree of accuracy, and I would recommend some light .38 loads for that not unpleasant chore. Your 642 will probably become one of your favorite handguns.
A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.