I notice there isn't a whole lot on this topic so I decided to spend some time and make a thread going through this subject.
Before deciding to carry pepper spray you should look into your laws and see what is and is not legal. QKshooter made a thread about which states are legal and aren't legal and their restrictions here is the link: OC Pepper Spray - Is It Legal In Your State? The main legalities to look at are:
-(UV)Ultra Violet Dye: A lot of states allow it, here in Wisconsin however, it is illegal. It is a great way to help police locate the suspect.
-Percentage of OC (Oleoresin Capsicum): This is the oil that is extracted from the peppers. It normally ranges from 2%-20%. Note that the percentage does not necessarily mean it is any hotter, there are many 2% sprays that burn much more than 20% sprays. Most states allow up to 2%, here in Wisconsin we can have up to 10%.
-CN Tear Gas (alphachloroacetaphenone): It is a strong irritant that is occasionally added to OC spray. Here in Wisconsin, it is illegal.
-Amount you can carry: You have to look at how much you can carry, in Wisconsin I believe you can have up to 4 ounces. You can carry separate cans but the overall amount must not exceed that.
-Safeties: Most states require that you have some sort of safety on your pepper spray and a good idea even if not required to prevent accidental discharge. Flip top is the most common type.
-Expiration date: This is something to keep in mind that is often overlooked when ordering online. If there is no date on the can it cannot get shipped to Wisconsin. Regardless if it is legal or not to get shipped to your state, you should be aware that the shelf life is typically 2-5 years.
How hot the actual OC spray is is measured in Scoville Heat Units (SHU's). The more SHU, the hotter the spray is. This is why I said the actual percentage of OC does not necessarily play a role in how hot it is.
Pros and Cons of the different types:
There are 4 main types of pepper spray. They all have their pros and cons. Youtube has quite a few videos so you can see exactly how each one sprays.
Stream- This is one of the most common types. It shoots a narrow stream and is typically pretty accurate and can shoot up to 15 feet. There is not a great deal of blow-back, however you still do not want to be shooting it directly into the wind. A pretty decent choice if you are looking into buying.
Gel- This is one of the newest types to come out. It shoots a narrow stream of GEL instead of spray. It is very sticky and isn't easy to wipe off. It is much more unlikely to get any blow-back compared to the spray/stream. A very good choice if you are considering buying some.
Foam- Foam has a wider spray than the stream/gel types. The only downfall to this is it is very easy to wipe the majority of it off and it is not wise to be in contact with the BG when he/she is sprayed, as the foam will easily get on you also. There have been reports of the foam being wiped off and flung BACK at the victim, but this is very unlikely and not something you should use to rule out this option.
Fog- Last but not least we have the fog type. As the name suggests this is a widely dispersed spray. Blow-back is extremely possible with this type and should not be used in any windy conditions if you do not wish to get any on you. This is, however, the best option for indoors/multiple subjects because of the large area it sprays.
I'm also adding the Kimber Pepper Blaster. It contains 2 shots and has a decent range. It supposed to be pretty powerful stuff. There are videos on Youtube of people getting hit by this so you can see what it is capable of.
Also adding the Fox labs pepper spray grenade. The link is on the post from Badey below. Could be useful to add to the collection of home defense products.
Another tip to add to this: Never keep you pepper spray in the glovebox or trunk of a vehicle. It can get too hot and that is the last thing you would want... Anywhere else in your car should normally be OK however, even on hot days.
There are many good options for which brands to go with. Some of the most popular include Sabre red, Fox labs, and MACE. I would recommend FOX labs over any. It has many good reviews and is known as some of the hottest sprays you can buy.
There are many good reasons for both men and women to carry OC spray. I'm sure a lot of you have been in/seen/heard of situations where you don't know if it would be justified to shoot or not. Pepper spray has offered a non lethal solution to this problem. If it is your life in danger, spray and immediately run (if possible). Keep in mind that the spray will sometimes be less effective on BGs who are intoxicated. It always works amazing on dogs and bears and pretty much any animal that wants to cause you harm.
I'm no expert in this but hopefully this answered a few of the questions I have seen people asking lately. If you see anything missing feel free to comment.