DroneShield! Protect Your Privacy
http://droneshield.org/Home.html
DroneShield is a low-cost, easy-to-use device that detects the presence of nearby drones (including RC helicopters, quadrotors, etc) and issues alerts via email, sms, and a flashing light. The goal is to help preserve privacy from low-cost remote-control air vehicles with video cameras.
DroneShield includes a microphone that listens for sounds of drones. Each DroneShield contains a database of common drone acoustic signatures so false alarms are reduced (IE ignores lawn mowers and leaf blowers) and in many cases the type of drone is also included in the alert.
And now for the best part...they are porting it to Raspberry Pi!
I have signed up to volunteer my time to help assemble, load software, test and debug...
Does anyone else find this project as awesome as I do 
?
Jeff
