The first thing I would like to say about this subject is that if you are thinking of carrying a knife and you aren’t an extensively trained martial artist of some sort, don’t carry one as a weapon. They are tools, but as weapons they require much skill and the intent to kill, so don’t carry one unless your trained for it. You need to get to close to your enemy and it is just to risky, chances are you will have it taken away and probably get stabbed by it.
Now that is not saying you shouldn’t train minimally for knife fighting, they can be a field expedient weapons and you should be familiar with them, but they don’t make a good primary defencive weapon, offencive maybe.
The first one I would like to cover is pepper spray, or mace. My favorite is bear mace but it may be illegal in some states if you use it on a person (Officer: why do you have bear mace in Vegas?) Mace tends to be illegal in some states also so check with your local laws, city, state and county laws. The good thing about pepper spray is that if you get it taken from you, it is just going to hurt if they use it on your, you won’t die like a knife would.
Some brands and grades of pepper spray are better than others but even the little key chain stuff is going to inflict a fair amount of pain and blindness, so with pepper spray you can go cheap and still get a half decent product. My suggestion is though, don’t go cheap. I personally like the Cold Steel brand as it is broken down to the smallest molecules possible. This makes it the only pepper spray available to civilians that I would trust against someone high in drugs. The reason being is that when the molecules are broken down, they penetrate the skin and membranes better, this causes the tissue to swell, therefore if someone can handle the pain, big deal they still will not be able to breath or see due to the swelling. Also (like bear mace) it can have a thirty foot range due to it being made of gel.
Another option is, stun guns. These are the close range electronic zappers that involve you getting close, but nonetheless they are quite effective and easily concealed. I must warn you though, some of the cheaper ones you get from the smoke shops and such are no good. There is a lack of quality control with these and tasers, so you should shop around carefully. I suggest a voltage no less than 500,000 volts. Reason being is in my younger more reckless years me and my buddies had a couple that where less than that, made for some really good truth or dare games, but truthfully they only hurt enough to piss someone off even if they are sober.
The other electronic option is tasers. these have projectiles that shoot out and send electronic pulses through a wire attached to the gun, they are far more effective using less voltage, so 100,000 volts is fine since the barbs penetrate the muscle and cause it to seize up. Problem is, they require some training to be effective and are quite expensive, some costing a few thousand dollars. I feel that it could be cheaper to buy, take a training class, and get a permit for a pistol than use this, but hey we are talking about non-lethal weapons.