Typically they are lightweight and offer you a super advantage to any attacker.  Most have a pop off cap that prevents accidental firing and a quick and easy spray activator.  Just attach to your key chain and you will always be secure when getting in your car, home or office.  

Don't let the size of these little canisters fool you... it will disable any attacker for 20 to 30 minutes.  It is a great deterrent for humans, dogs, or any other wildlife.   I am going to make it a point to give these away to family members this holiday season.