Tunnel Surveillance Monitor

Embedded in the dimly lit tunnel walls, these rectangular black monitors project a faint blue light from a narrow slit across their surfaces. Their seamless obsidian casings blend into the stonework, save for the telltale glowing veins tracing the edges. The devices remain dormant during routine passage but activate at irregular pulses, scanning movement and relaying data to unseen operators. Their low-resolution imaging strips detail from figures, leaving only silhouettes and flickering signals—ideal for detecting unauthorized travel without revealing watchers.