Stun guns can induce pain through the quantity of electrical charge that is transmitted to the body. This is measured through microcoulombs, the only true measurement of a stun gun's strength.
Some stun guns claim extremely high voltage - up to 100 million volts. While this sounds impressive, voltage measures the force of the electrical current, which does not indicate the pain induced to the target. On top of that, the maximum voltage that can be reached for the standard size of stun gun is 30,000*.
According to the National Institute of Justice, with microcoulombs at 0.5, subjects reported pain, and intolerable pain was reported at 1.0 microcoulombs. That's why all of SABRE's stun guns produce at least 1.0 microcoulombs of electrical charge.