Night Sticks
The oldest weapon in history is the club - for good reason, as it is both simple and effective. The modern equivalent, often seen in the hands of law enforcement and private security, is the night stick or baton. While the mere knowledge that you are armed with such a weapon may deter some criminals, a baton requires training to use effectively. A potential attacker will likely be able to tell if you are uncomfortable or unskilled with the use of any weapon, and in that case you may as well have just armed him with it.
The main advantage of the night stick lies not in its striking power (although due to the leverage available this can be tremendous, enough to break limbs and potentially be fatal) but in its reach. It allows you to remain out of reach of an attacker while still maintaining the ability to strike him. However this can turn into a disadvantage in a cramped situation (such as in a vehicle) or if your attacker manages to get close to you - you will not have room to effectively use the baton in these cases.
There do exist compact batons, often referred to as " kubatons' or " kubotans' . Unlike a full length telescoping night stick (which cannot be carried concealed without a permit) the kubotan is only five or six inches in length. They are used differently from the conventional night stick. The point is usually used to " stab' an attacker at sensitive pressure points , which is highly effective because it concentrates the force of the blow on a small area - there are also currently no legal restrictions on kubotans and they are often sold in keychain versions.