LAS VEGAS — What do you do when the target you’re spying on slips behind his home-security gates and beyond your reach?

Launch your personal, specially equipped WASP drone — short for Wireless Aerial Surveillance Platform — to fly overhead and sniff his Wi-Fi network, intercept his cellphone calls, or launch denial-of-service attacks with jamming signals.

These are just a few of the uses of the unmanned aerial vehicle that security researchers Mike Tassey and Richard Perkins demonstrated at the Black Hat security conference here Wednesday.

At a cost of about $6,000, the two converted a surplus...