Most car sunroofs and rear windows are made of tempered glass. To discern the type of glass in your vehicle's side window, examine the bottom corner for any indication. You might find a label stating 'tempered' or 'laminated.' In the absence of a label, lower the window and observe it from a top-down perspective. A seamless, single-layer appearance indicates tempered glass, whereas a multi-layered appearance with a noticeable ridge suggests laminated glass. Window breakers are typically effective on tempered glass. 

We ask that people stop spreading this misinformation that you can simply take one last breath as your car fills with water, the doors equalize in pressure, and then you open to escape. Myth Busters did 2 episodes to demonstrate this and would have died both times if they didn't have a safety backup diver. Don't chance you life on your single last breath of air. Roll down or break your windows early and escape as quickly as you can, but do so only after you've removed your seat belt.

The Transportation Security Administration has not assessed this particular safety tool nor included it on the prohibited items list for Carry-on. While it is compact, it doesn't mean it's undetectable by X-ray machines. Given the fact that it houses a blade, our suggestion is to stow this tool in your checked baggage to prevent possible seizure.