The 'kubotan'. You know, those self-defense keychains that look like a spike...
Still have no idea what I'm talking about? 'Kubotan' is a registered trademark of Takayuki Kubota, who developed the device as a tool for police officers in the 1970s. Overall it is a very handy, practical self-defense tool.
quick discalimer: understand that a 'kubotan' is a tool - and all tools are secondary to your main weapon - your mind/heart.
The 'kubotan' is fairly discreet and can be very un-assuming. They can be made out of wood, plastic acetate, & metal (aluminum is common). Most are rod shaped and vary in terms of length, taper, thickness and weight.
Using a 'kubotan' is very natural. However, just like all tools, you should seek proper instruction.
TIP: once you learn the 'kubotan', many everyday items can be substituted for one, such as: pen/pencil; chopsticks; flashlight; smartphone; salt/pepper shaker; screwdriver; etc.