Not sure about that being feasible to detect things of that nature with this system. For example you can build a mini quadcopter (size of a bird) weighing 5-800

Not sure about that being feasible to detect things of that nature with this system. For example you can build a mini quadcopter (size of a bird) weighing 5-800gms that can provide 2+KG of thrust. Back of the napkin math says a 400gm m67 grenade is easily within the payload capacity (Assuming 70% throttle to hover all up payload would be 1400+-gms). I would be very impressed if this could differentiate "bird sized flying objects" from birds. With that in mind I think we can be glad that complicated plots of that nature stay in the realm of James Bond rather then reality. Also I think the Boston bombings show that bad people don't need complicated technology to do bad things.