I have pepper spray for safety and always end up leaving it home or in car (unless I feel particularly uneasy) because it’s clunky/large/annoying to deal with on keychain daily.
The following incident occurred before call phones were in common use: I used to be in law enforcement in Florida (in a very small town), but never had to use my pepper spray. I moved back to Chicago (where I'm from) to go to college (as an older, returning student). Well, I still had my old can of pepper spray, so I used to carry it with me just in case.
One day riding the 'El' a 40-something year-old male started threatening to rape and murder these two attractive 14 year-old girls as soon as they got into the train car. At one point everyone in that car (all elderly women) moved to the opposite end of the car from where the suspect and potential victims were. Then, the girls got up to move seats - one sat next to me, and the other behind me (at this point I knew something was going to happen, so I reached into my pocket and armed my pepper spray).
The suspect stood up and pulled out a large pocket knife, which he then opened and said to the girls, "I'm going to rape you both, kill you, cut you into pieces and send your heads to your mothers in a box". I told the girls to run to the end of the car (as far away as possible, and not to intervene in whatever was going to happen - to just stay safe). I stood up and moved to the aisle, and looked the suspect right into his eyes to let him know I was strong and serious. He then said to me, "nice going, you stupid b*tch - now I'm gonna cut you too".
He advanced toward me with his knife extended in front of him, and I pepper-sprayed him in his face, and then kicked him hard in the stomach to knock him backwards. This was met with a barrage of vulgarities, and now he was furious... He moved toward me again, and I kicked him in the crotch. He then slashed at me and I put my arm up to protect my face/neck - he cut through my heavy wool coat down to my arm, which was cut as well. I then sprayed him in his eyes (he was wearing sunglasses, but now they had slipped down enough for me to get a good shot).
This fight went on all while the train was moving along, with the suspect landing a few knife cuts on me, and me continuing to pepper spray him - in his mouth, in his ears, even up his nose when I could. As we're pulling into the next station I could see 3 police officers (with a police dog) who caught a glimpse of us fighting, and out of the corner of my eye (I was still fighting the suspect) I could see them running along the platform toward my car.
As the train slowed, I again sprayed the suspect, and now the canister was completely empty. So, I kicked him once again in the stomach area, knocking him backwards and causing him to fall on his behind with his back up against the wall in a nook that has no seat and is used for those with a wheelchair. Just then the train stopped and as soon as the doors opened the police rushed in, and I quickly told them what had happened, and that the suspect still had the knife on him.
They drew their guns on the suspect, but he refused to give up his knife. They then said, "the knife, or we're going to release the dog". The suspect still refused, and the let the dog loose - which of course resulted in him being severely bitten (there was a lot of blood as he was being torn to pieces by the dog) until at one point I see the knife go flying in front of him and hit the floor with a loud 'clank'. They then pulled the dog off of him, and too him into custody (and got him an ambulance).
Once out of the car and on the platform the 2 girls ran over to me and were hugging/clinging on to me so hard - they had obviously been terrified. A female police officer was sent over to take our statements, and she got an ambulance for the girls as well as they were just an emotional mess. Even though I was pretty bloody, my wounds had stopped leaking so I refused medical attention (I went to my own doctor later that day).
The girls and police were so thankful, and the girl's mothers were on the way to pick them up (the police had contacted them ASAP).
So, the suspect had a prior criminal record, and had been drinking and using drugs before the incident. That's one of the reasons the pepper spray wasn't as effective as it could have been - the other was that the canister was over a year old. So, replace your pepper spray yearly, never ever 'test' it, and keep it someplace easily accessible - in a pocket or in your hand when you walk; ideally not on your keychain (as your keys will interfere with its use should you need to spray it). Don't be afraid to use it if you need to; when someone attacks you (or you're protecting someone else) you cannot hesitate even for a brief second - an experienced offender will take advantage of that 'opening' to gain control of the situation. If you use it hold on to the canister tightly so the suspect cannot take it from you, and aim for the mouth, eyes, up the nose, and in their ears. Lastly, pepper spray should be used to disable the attacker which will give you time to get away - and getting away should always be your objective (unless like my situation you just cannot retreat).
Always take your pepper spray with you - it won't be of any use if you leave it at home or in your car.