Glass breaker

A glass breaker is a small hand tool designed to aid in the emergency extrication of occupants from a vehicle. Most glass breakers contain a sharp pointed metal tip for breaking tempered glass and a sharp knife for slicing through seatbelts. Glass breakers are also built into other tools, such as flashlights or multitools. Unlike bus mallets, glass breakers are smaller and generally privately owned. There are many variations of glass breakers on the market. One variation found in glass breakers is the material of which the metal tip is made from. Although all glass breakers are made of strong materials, some glass breakers make breaking glass easier than others, depending on the hardness of the metal that the tip is made of.  Some sources have found that tungsten carbide tips make breaking glass less difficult. However, laminated glass cannot be broken by any glass breakers on the market.  Glass breakers are only effective on tempered windows. 
Spring Loaded Glass Breaker.
Glass breakers come in two styles, hammer and spring loaded. Spring loaded glass breakers take away the need to swing a tool to break a window.  The metal tip is simply held up against the window and either a pin is pulled back and released to activate a spring, or the spring is pulled back by the user directly.  This type of glass breaker is designed to be used underwater or to simply reduce the amount of strength needed to shatter a window.  When a car is submerged underwater, a hammer style glass breaker becomes significantly more difficult to use.  While this type of glass breaker is convenient, most spring loaded glass breakers are limited to the force of the spring. This could limit the users ability to break the glass.
Larry Goodman's Safety Glass Breaker.
A similar device invented by Larry Goodman instead utilizes a .22 blank cartridge detonated with a spring loaded firing pin, relying on expanding gas rather than spring tension to drive the striker. This is less susceptible to mechanical failure and applies a much greater force on the window increasing the likelihood of success.