Thanks, good demo on the Mythbusters youtube video. Another good video links from there — Escape a Car Underwater
What I liked about that video is they discuss and then demo the physics of opening a door underwater and during one exercise they fail and go to the air regulator. They also demo a window punch to shatter the driver side window, thus immediately equalizing pressure and the door opens.

I already have window punches, in Molly loops on the drivers side visor, and on the vest, but in the video, he had gone through the evolution several times, so he had some familiarity or a comfort level, he knew what to expect, kind of, and he already had it in his hand. In EMS and Fire Rescue, I have them in my scissors pouch and turnout pants pocket. We're using it from the other side of the equation, "controlled" patient access and extrication, not inside the car filling with water. I'm thinking the rock hammer, or like, is more gross motor skill, catacholimine soaked compatable? I found a mount that I think will keep it secure in a roll over, (only one way to find out, and I don't want to be that sure), yet easy-ish access. Combined with a military Rescue Tool 511 600 524 6924, with duess (?) key, basicly about a foot long, T ish handle, with a V on the other end with replaceable V blades at the apex. Lite enough to be secured with velcro, stupid simple enough to work. ( the one Colonial Knives sells is made in the PRC, I'd rather have US made, if possible, sources?) Secured to the console by my right knee, and as they aren't vest-able, the rip shears and window punch remain on the vest as back up. Make sense?

Regards, Jim

ETA: Just FYI, incase yous don't already know, but as the dude in the video discovered, that with that particular design of punch, your hands tends to follow the punch through the glass leading to cut hands. Gloves should be used. Also, in more terrestrial environs, dust masks and glasses/goggles should be worn by rescuers and patients (assuming the patients are not on non rebreathers already) when we pop windows, as glass fragments can be aerosolized, and you do not want to breath them, or get them in your eyes. This is espicially true when sawing the windshield. JMH

What makes sense to me is a device inside the vehicle that doesn’t require a swing to strike the glass, such as a hammer would require. One of the spring loaded window punches makes more sense; press against the glass, the spring is activated and shatters the (non-laminated) glass. I have a Resqme Seatbelt Cutter and Window Glass Breaker dressed in yellow inside the car and another on my keyring. Break the glass and either open the door to swim out or go through the now open window (with increased risk of laceration).

In one run-thru in the video link I posted above they also started opening the door immediately on water entry which might work depending on the vehicle and mindset of the individual. Things go wrong at the worst possible time and the door not wanting to open after you are submerged would be typical... If the door won’t open on the surface, I’d immediately shift to breaking the glass.

Murphy. Just my experience, with the key ring things with the window punch and webbing cutter, I tested the punch against the sole of my boot, just to see if it would work, the thing fell apart. As always, your mileage may vary, and use what works for you.
Thanks, Jim

I had a resqme with a spring failure. It just started to rattle, because the spring was loose. Tested it; no tension, nothing.

That why i got both simple hammer and a spring loaded window punch.