A CIA official who spoke with the Associated Press on the condition of anonymity says the Secret Service is looking at signal jamming. The source noted that service members flew drones in the wee hours of the morning, from 1 a.m. to 4 a.m, and then likely used anti-drone countermeasures against their own vehicles to see if jamming worked. The AP suggests that the tests were done so early so as to minimize any unintended effects on nearby electronics. Remote controls for drones use radio waves just like WiFi does, and jamming the GPS signal for a drone could also jam the GPS signal for nearby cell phones. The jamming technology the Secret Service utilized most likely isn't that revolutionary, as personal anti-drone jammers already exist. However, they're generally illegal to use, unless you're the federal government, which the Secret Service most decidedly is.