A simple superior tool about the size of a stubby pencil that punches a tiny depression in metal. It’s used to start a hole, or mark a point. But unlike standard punches, which you need to hit with a hammer — whose impact usually misalligns the spot you intended to punch — this one gets its punch from a tiny internal spring that flexes as you press the tip down. You simply press the punch where you want a dent and there it is exactly. A classic.
We in the rescue trade also use these pretty routinely to safely remove the glass in automobiles. They work particularly well on the glass in the side and rear windows and leave all of the little glass bits intact in the window frame until you gently remove them with gloved hands. The bits then go where you want (generally) and not on your patient. I assume that keeping one in your car would let you punch out your own windows in case of emergency. Just remember that it is key to use the device on the lower corner of a window or the glass can shatter and go everywhere.
— J. James Bono