For those looking for an impromptu self-defense tool, consider this Tactical Pen by Gerber. While there are many other 'tactical' pens on the market, this pen has the high-powered ability to break through windows.
Other pens are 'tactical' in the sense that they typically contain or conceal a switchblade inside; this particular pen does not contain a blade but a glass-breaker tip made up of tempered steel. This pen could also be used as a stunning tool against attackers. The pen is unlike others in that it is not designed as a weapon, but a tactical piece to defend or remove someone from danger. Other pens may be seen as weapons with a more clear intent to harm.
This pen also features a 'Rite in the Rain' cartridge that works in all conditions -- wet and dry, and upside down. The pen is simply a regular pen that can be carried with you at all times. This pen can be purchased online for around $45.