The world's smallest pistol is the Kolibri (hummingbird) designed by German watchmaker Franz Pfanni. Can it protect you or is it just very very very cute?

Place it next to an infant's skull and pull the trigger and tell me how cute it is.

It's a gun.  It works.  Not cute to me.

It's an assassin's weapon.  People have been killed them them.  Killing someone with that small a powder charge and shell requires shooting them through the eyeball, or placing the barrel of the weapon on the back of the head, right below the ear and below the lower edge of the temporal bone.  The noise of the discharge sounds like someone putting a tack into a wall to hang a picture. 

While all firearms are potentially lethal (actor John Eric Hexum died when he fired a pistol fitted with "blank" cartridges at his own head), it appears the Kolibri would make a poor self-defense weapon.

Reports on the internet suggest it fired a tiny bullet at a fairly low velocity. In very rough terms, the lethality of a bullet depends upon the energy it delivers to a target (i.e. large fast bullets do more damage than small slow bullets). Also, the Kolibri did not have a rifled barrel, so its accuracy dropped off immensely with range.

Using a Kolibri as a self-defense weapon would depend upon the target being very close, very still, and the fired bullet striking something vital. Otherwise, the chances are a Kolibri bullet would either miss, or deal a non-fatal wound to periperhal tissue. After which, the undeterred assailant would probably be extra nasty for having been shot at (and possibly wounded).

it might still protect you since it has bullets in it

Thank you for your reply Sharonna and the graphic.

 Wow!  So you are familiar with it then CSV? Thank you for your helpful reply and Happy Monday to thee! :)

Mahalo for your thoughtful and helpful reply OS! :)

Only if the assailant is up close and you can hit a vital organ. Apparently it isn't much good for distance. Thank you for your reply pearl! :)