On a recent episode of the Discovery Channel's Mythbusters program, Adam and Jamie tried to find out how to escape from a sinking car. They and I were surprised that the only ways they were able to break the windows of a car door that had been submerged in water was with one of the emergency car hammers (such as a LifeHammer). This episode doesn't appear to be online, but general tips on safety relating to flooded cars are here.They first tried to determine whether it would be possible to roll down manual or electric windows given the pressure at just two foot of water depth. They weighed down an automobile window with 350 pounds of weight, and with both types of windows they couldn't get it open; with the manual variety the gear slipped. Then, they tried to break a car window that had been put into two feet of water. Neither car keys nor steel-toed boots worked. Then, they tried two types of car escape tools: something that either was or looked like a LifeHammer, and a similar spring-loaded tool. To their surprise as well as mine, both worked as advertised.