Why We Like It? With similar capabilities as the shooting stun guns sold by TASER, the Dual Defense system costs approximately $300 less. In addition to less expensive startup costs, replacement ammo is also less costly.The Dual Defense System is a combination of two units: the Thunder Strike™ stun gun and Lightning Strike™ cassette. The Thunder Strike™ stun gun provides the base and can work as a regular contact stun gun by itself. When the Lightning Strike™ cassette is attached to the front of the Thunder Strike™ stun gun, the unit works as a Dual Defense System. The Lightning Strike™ cassette can shoot two missile-like probes in a split second up to 17 feet in order to close the distance between you and the attacker, leaving you with plenty of time to get away and call for help. The unit is small enough to fit in a purse or bag and comes with a 9V battery and target for practice.