Explore a conference talk on multi-receiver real-time physical intrusion detection using GNU Radio and USRP N310. Discover how indoor digital communication, like Wi-Fi, can be utilized for creating a "burglar alarm" system. Learn about leveraging internal radio receiver signals, such as PLL or AGC blocks, to detect channel changes caused by moving targets within the physical space. Examine a practical test setup using GNU Radio and Ettus USRP N310 hardware for both transmitter and receiver. Gain insights into the system's performance through a coverage map demonstration in a large building environment. Presented by Daren Swasey, Todd K. Moon, and Mirelle Despain at GNU Radio Conference 2021, this 20-minute talk offers valuable knowledge on innovative approaches to indoor security systems using software-defined radio technology.