One of the oldest weapons if mankind is the simple knife.

Easily manufactured at home, or a prison cell form what is available.

Small and concealable.

The knife can not be regulated from existence.

The effectiveness of a knife is not disputed. When an artery is severed life is draining out in minutes without serious medical intervention. a severed aorta or heart or other major blood supply vessel is beyond the help of man.

Severing the tendons disables the limbs from effective operation.