This Halloween Skull Uses 24 GHz Radar to Track Three People Through Its Plastic Head, With No Camera

The sensor choice is the trick. In Part 1 of his build series, Jon is blunt about it: “There is no camera, and no PIR motion sensor either.” The radar module sits inside the head and “talks to the RP2040 over a simple UART connection.”

The eyes are rings of addressable LEDs, and they do the reporting. There’s “one lit LED per person it can see.” The color tells you how close you are: “Green when you are far away, shifting to red as you get closer.”

The skull has three moods: “asleep, watching and hunting.” Asleep, the eyes show “a slow pulse.” When it hunts, two servos turn the head in “a sudden predator strike.” Part 2 describes that move plainly: “It accelerates harder and harder, then stops abruptly.”

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And it loses interest. “Stand still for thirty seconds and it gets bored and goes back to sleep.”

The SkullHead2026 code is on GitHub under the MIT license. The parts list names an RP2040 Zero board, a Keywave KW307 radar, two MG995 servos and two 7-segment WS2812B LED discs.

The earlier years show how he got here. His 2023 build was a Guy Fawkes mask on a Raspberry Pi Pico with three ultrasonic sensors “spread 34 degrees apart,” and “Three sensors, two LEDs and two servos on flying leads added up to 46 connections.” In 2024 a skull got two round 1.28-inch LCD eyes, and how did it sense people? “It doesn’t.” The 2025 build was a ghost on an AMOLED screen behind glass, because “black pixels don’t reflect, so only the ghost appears.”

Four years of these builds trace a path that many hobby projects follow: three ultrasonic sensors and 46 hand-run wires in 2023, then no sensing at all for two years while the eyes got better, then a single radar module talking over one serial link in 2026. The open question is what he does with the radar next. He’s already said the plan is “a Christmas snowman that watches people move around the room and waves at them.”