Not every jurisdiction requires that every will be witnessed. Some states, like California, authorize unwitnessed holographic wills if they are written entirely in the handwriting of the will maker, who is known as the testator. Notarizing a holographic will is not required, but it also doesn't invalidate the will.
If your state does not accept holographic wills, you can still write out your will by hand if you get witnesses to sign after you. Witness requirements vary among jurisdictions. Most states accept a will -- handwritten, typed or printed -- with two or three witness signatures. Notary signatures on witnessed wills are generally not required, but do not invalidate the will.