This is a small but potentially seriously valuable tool in case you or someone else is involved in an auto accident.  As you can see in the photo there is a car key which lets you know this is not very large and is meant to be used on a keychain, which is likely the best place to keep it because if you are in an accident having access to the key still being in the ignition is more likely than any other place in my opinion.  It has two devices to help you out if you are in an automobile accident or if you are trying to help someone else that has been in an accident.  The first is a glass breaker.  Auto glass needs to be strong to undergo the rigors a car goes through, so it is not always easy to break.  This tool uses a self-loading spring action with a glass breaker spike inside the end of the round part on the bottom.  You push the bottom against the glass which takes 12 lbs. of pressure to accomplish which means you need to press it fairly hard, then when it reaches that level of pressure it releases a spring loaded spike which will cause auto glass to shatter thus allowing you to escape an accident should a door be jammed for example.  Or help someone else to escape a similar situation. This means you only have to be able to press this device against the glass hard enough to activate the spring, not hit it with a standard glass breaker with enough force to cause it to shatter.  I would suggest pressing the glass breaker up against a piece of cardboard or something similar so you will get an idea how hard you will need to press this against auto glass to get it to shatter if and when you actually need to use it, but not against a hard surface to prevent damage to the spike inside.  By having this on your keychain it is far more likely you will be able to reach it if sometime you really need it.This is made not made to break out a windshield.  Those have laminates sandwiched between two pieces of glass at will be held together by that plastic laminate.  The other windows in a car will shatter in to hundreds of tiny pieces when broke  It just takes enough force to get them to break.  The spring loaded spiked inside this is enough to cause the entire window to shatter which is what you want, especially if you are not in a condition to hit the window really hard with some other glass breaker which depends on you having enough strength after the accident to still have an arm free, reach the device and kit it hard enough to work.  I think you have a much better chance with the spring loaded devices as used in this tool.The second part is the seatbelt cutter.  There is a sharp blade that is inside the curved part of the unit.  It has a cap on it which needs to be removed to use, however when you have a key attached to it that gives you enough leverage to easily remove the protective cap and then you can cut yourself or someone else free from their seatbelt should you be unable to unbuckle them. You simply slide the seatbelt between the gap when the cap is removed and slide it to have the blade cut the belt, this is also made to prevent accidentally cutting yourself as the blade is inside the unit. I have not tested the blade on an actual seatbelt as I would not want to dull the blade in case I actually needed it.  It appears sharp enough to do the job though.  And while I usually have a sharp knife nearby if in an auto accident things get thrown around and the most likely item you will be able to reach is this tool attached to the key in the ignition.  It is purely a safety tool that hopefully you will never need.  But if you keep one on your keychain it will be there just in case you, or someone else you see in an accident needs it to escape a serious automobile accident.I don't see how you can afford NOT to buy one of these.  If you ever use it just once it will have been worth many times more than the price paid.  How much are the lives of yourself and your family worth to you?  How much would you be willing to pay to be able to cut your child free after a car crash to get them to safety.  Or to be able to break a window to escape a car you were trapped in?  I do not sell these and I hope nobody gets in a an auto accident.  But chances are that some of us will at some point and having one of these devices might make the difference between being able to escape or not.  Cheap insurance you hope you never need in my opinion.