As a one of many ways - use high intensity ultrasound signal modulated with garbage to overload mics of that spy gadgets.
However, I think, best way is a microwave gun. Because damage is nearly instant and irreversible. Unfortunately, affordable microwave gun made from microwave oven parts is not a compact thing, so hardly it could be used stealthly. :)
As a one of many ways - use high intensity ultrasound signal modulated with garbage to overload mics of that spy gadgets.
However, I think, best way is a microwave gun. Because damage is nearly instant and irreversible. Unfortunately, affordable microwave gun made from microwave oven parts is not a compact thing, so hardly it could be used stealthly. :)