http://www.defensetech.org/2016/05/16/battelle-fielding-100-drone-zappers-to-pentagon-homeland-security/
The drone-zapper disrupts the radio-frequency between the drone and its operator, causing it to go out of control, or I guess they hover themselves to a safe landing when control is lost.
The drone industry is expected to reach $21B in annual sales within the next 5 years.