Short-range air defense (SHORAD) is going to be a huge growth area for defense contractors over the next several years.
I wonder if we can repurpose mm-wave 60GHz panel antennas and SDRs for cheap short-range radars. Then combine with a commercial infrared camera for multi-mode target acquisition. Put those on a mount with servos to control a PKM or M240 machinegun, and mount the whole setup on the roofs of buildings. Critical infrastructure anti-drone air defense guns at fairly low cost.
Leaving weapons unattended like that is a recipe for disaster. Even worse if they're network-connected (look at the tons of insecure IoT devices already out there).