In "A Taste of Armageddon," Kirk and company find that the Eminians are in a sort of "computer" war with the Vendikans. In the episode, Eminian weapons are displayed and used, but, unlike a Federation phaser, do not produce a visual stream of energy when fired.
The energy, or whatever it uses, is invisible to the human eye, and quite likely also the Eminian eye.
What sort of weapon is it? If nothing in canon speaks to this, non-canon sources are acceptable.
Captain Kirk brandishing two of the weapons while on Eminiar VII