Pepper spray is the most popular self-defense weapon, but it is not legal in all states. At the time of publication of this writing, common pepper spray law was that you are allowed to carry it in all states.
In California, the largest can of pepper spray you are legally allowed to carry is 2.5 oz.
In Michigan, New York, Wisconsin, and Hawaii, pepper spray law says you are allowed carry it. There are, however, concentration limits and other restrictions. If you live in one of these states or plan to visit, be sure to carry a pepper spray that is sold as “Michigan Formula,” “Wisconsin Legal Pepper Spray,” and so on.
If you live in or plan on visiting Massachusetts and you want to carry pepper spray legally, their pepper spray law says you must get a FID (Firearms Identification Card). All you do is go to your local Massachusetts police station, show two forms of ID, fill out a form, pay $2, and wait a week. When you get your FID, keep it on your person (and of course, to make the FID useful, keep your pepper spray on your person as well).
Pepper Spray Litigation
From time to time, civilians and law enforcement officers have managed to use pepper spray excessively or irresponsibly. Even though pepper spray is non-lethal, it does hurt to go through getting sprayed with pepper spray. If you feel you have been unfairly attacked with pepper spray, you can force litigation.
Concerned citizens across the country have also noted that police offers have been known to use pepper spray on people when use of it was clearly gratuitous. Litigation has been pressed, and the media have touched on the subject to a small extent. As a result, the Justice Department commissioned a report about the benefits and dangers of pepper spray, resulting in a more education law enforcement system.