Irish B. If you were serious about the strings, I would check your state laws. Your system could meet the Legal definition of a spring gun. Spring guns are generally illegal and could get you in a world of hurt.
One of the neatest nonlethal systems I have ever heard of used by a former AF special operator.
He obtained a surplus air craft photoflash unit. It put out about 10 million candles.
When his storage shed was being broken into on a regular basis, he rigged the unit go off when the door was opened. The unit took about 10 seconds to charge and he had switch to deactivated it when he opened the door.
About 2 weeks after he installed the unit someone broke in and the unit went off. His neighbor. about two doors up, suffered from temporary blindness.
He never had another breakin.