UFO reports sometimes cite an "electromagnetic field anomaly" measured near a sighting, implying something unexplained. In practice, handheld EM meters are extremely sensitive to ordinary interference: overhead power lines, cell tower transmitters and even a nearby car's ignition system all produce real, measurable fields that fall off with distance according to well-understood physics. This simulator places three such sources on a map — a power line (a line source, falling off as 1/r), a cell tower and a vehicle (both point sources, falling off as 1/r²) — and lets you drag a measurement probe anywhere to see the combined reading. Move the probe around and watch the "dominant source" readout switch: the field always tracks whichever mundane source is closest and strongest, never appearing uniform or directionless the way an unexplained field would have to.