Source: https://mokxi.com/learn/arduino-halloween-props Updated: 2026-10-05 Learn # Arduino Halloween props you can build and test in your browser Intermediate Written by the Mokxi team, updated October 5, 2026 Start building free Open the editor Or see every lesson. - 261 parts on the bench - 31 boards running now - 1.00x real time, on every board Click to open it in the editor Prop 3 on a simulated ATmega328P. Click the radar to walk up to the box. Halloween ## Porch props you can test before you buy a part Halloween is the best excuse there is to build something with an Arduino. A box that throws its lid open when someone walks up, a skull that talks, a candy bowl that grabs back: these are the props people remember, and every one of them is a small, honest Arduino project. This page has five complete builds, the ones you would actually put on a porch or in a haunted house, and every one runs in your browser right now, on the real sketch, with nothing to install. The jump-scare box above is running on a simulated Arduino Uno. Click the radar sensor to walk up to it: the servo throws the lid open, the DFPlayer starts track one, and the two red eyes flicker until the lid shuts. Test the whole show here, change the timing until it feels right, and only then buy the parts. Ready to run ## The five props Each card opens the real wiring and sketch. Press Run, set off the sensor, and tune the timing until it feels right. Fog machine trigger A PIR fires a short fog burst through a relay, then cools down. Beginner Arduino Uno R3 Lights Sensors Parts - PIR motion sensor - Relay module - Ready and cooling LEDs Open in the editor Grabbing candy bowl A hand reaches in, a piezo cackles and a rubber hand swings down. Beginner Arduino Uno R3 Sound Sensors Parts - HC-SR04 ultrasonic sensor - Hobby servo - Passive piezo Open in the editor Jump-scare box Radar sees through the box, the lid flies open and the eyes flicker. Intermediate Arduino Uno R3 Sound Sensors Parts - RCWL-0516 radar - Hobby servo - DFPlayer Mini and speaker - Red LEDs Open in the editor Talking skull A servo jaw moves in time with a spoken line from a cue list. Intermediate Arduino Uno R3 Sound Sensors Parts - PIR motion sensor - Hobby servo - DFPlayer Mini and speaker - LED eyes Open in the editor Haunted window Lightning bursts on an LED strip while candles flicker on the sill. Intermediate Arduino Uno R3 Lights Halloween Parts - WS2812B LED strip - Short WS2812B strip for the sill - 10 k potentiometer Open in the editor Looking for something else? See every Halloween build. - 01 ### A fog machine trigger A PIR sees someone on the path and a relay presses the fog machine’s remote button for a short burst. A cooldown then keeps it quiet while the fog drifts and the heater recovers, with a green ready lamp and a red cooling lamp. This is the right first build, because it teaches the safe way to let an Arduino switch something big. - 02 ### A grabbing candy bowl An HC-SR04 ultrasonic sensor watches across the top of the bowl. When a hand reaches in, a piezo cackles and a servo swings a rubber hand down over it. Two readings in a row have to agree before it moves, so a stray echo never sets it off. - 03 ### A jump-scare box An RCWL-0516 microwave radar hides inside the box, because it sees movement through a thin plastic or cardboard wall. When it fires, a servo throws the lid, a DFPlayer Mini plays a scream from its microSD card, and two red eyes flicker. Then it shuts, rests, and arms again only once the porch is clear. - 04 ### A talking skull A PIR wakes the skull, its eyes light, and a servo jaw moves in time with a spoken line on a DFPlayer. The jaw follows a hand-timed cue list, and the DFPlayer’s BUSY pin tells the sketch when the line has really ended. It says hello once at power-up, so you know the speaker, the card and the servo all work the moment you plug it in. - 05 ### A haunted window A WS2812B LED strip along the top of the frame throws lightning in bursts of one to three flashes, the way real strikes flicker, while four more LEDs on the sill flicker like candles. A knob sets how wild the storm is. It is the lighting build, and the one that teaches how to run two animations at once without delay(). How it works ## Test it in the browser first A Halloween prop has one night to work. The usual way to build one is to buy the parts, wire them on the kitchen table, and find out on October 30th that the servo resets the board or the sensor fires at nothing. Mokxi moves most of that earlier and costs nothing. Each prop opens in the editor with its wiring on a real breadboard and its sketch in the code pane. Press Run and the firmware runs on a model of the Uno’s ATmega328P, with the servo, the relay, the sensors and the LED strip all answering the way the parts do. Click the PIR or the radar to make them see someone. Drag the ultrasonic sensor’s slider to move a hand. Turn the knob on the window. The Serial Monitor shows what the sketch is thinking at every step. Then change it. Make the lid stay open longer, give the skull a new line, make the storm purple. The sketch compiles in your browser in a second or two and runs again. When it does what you want, the same sketch uploads to a real Uno from the Arduino IDE. One thing to know up front: the simulated DFPlayer makes no sound. It shows which file it is playing and how far into it, so you can see the scream start on time and the skull’s line end, but the audio itself is for the real speaker on the porch. Under the hood ## How the talking skull keeps time, honestly There are two ways to sync a jaw to a voice, and it is worth knowing both before you buy anything. The first follows the audio. You rectify and smooth the speaker signal into an envelope, read it on an analog pin, and open the jaw as far as the voice is loud. Ready-made audio servo boards do exactly this. It works with any recording, but the jaw tends to chatter on every breath and hiss. The second is a script. You listen to the line once, note when each syllable starts, and write those moments down as cues: a time in milliseconds and a jaw angle. It takes a few minutes per line and looks crisp, because you decide when the mouth shuts. The skull here is scripted, and the course walks you through timing your own line. Safety ## Safety: mains, fog and relays Most of these props run from 5 V and cannot hurt anyone. The fog machine is the exception, so it gets the most care. A fog machine runs on mains power and heats fog fluid until it turns to vapor. Do not cut into its cord, do not switch its mains power with a breadboard relay, and do not open it. Nearly every fog machine has a wired remote whose button is a low-voltage switch: put the relay’s COM and NO contacts across that button, and the mains side never comes near the Arduino. Use a relay module made for the job, the kind with its own transistor and diode on board, so the Uno’s pin only drives the module’s input. Keep the fog machine’s nozzle where nobody can touch it, never leave it running unattended, keep fog away from smoke alarms, and keep it away from anyone with asthma. Two smaller rules save most porch props from failing. Give servos their own 5 V supply, such as a USB power bank, with its ground joined to the Uno’s: a servo that jumps hard can pull the Uno’s 5 V down far enough to reset it, right at the scary moment. And give LED strips their own 5 V supply sized for the LEDs, with a large capacitor across its 5 V and ground where it meets the strip. Buying the parts ## What you need to buy Nothing, to try them. To build all five, an Uno and a breadboard cover the brains, and the rest is a short list: a PIR motion sensor, an RCWL-0516 radar, an HC-SR04 ultrasonic sensor, two hobby servos, a single relay module, a DFPlayer Mini with a microSD card and a small speaker, a passive piezo, a WS2812B LED strip, a 10 k potentiometer, a few LEDs and resistors, and a separate 5 V supply for the servos and the strip. Each project page lists its exact parts and every connection. Course ## Build one step by step The Build a Halloween prop course takes you through all five in order: sense a visitor and switch something safely, move a lid and a jaw in time with sound, then light the scene. Each lesson opens the real build, asks you to run it and set it off, and explains the one idea that makes it work, with a check that goes green when you have it. Start with the fog trigger and you will have a working prop in under an hour. Start the Build a Halloween prop course FAQ ## Questions What is the easiest Arduino Halloween prop to build? The fog machine trigger: a PIR sensor, a relay module and two LEDs, with a short sketch that fires one burst and then cools down. The grabbing candy bowl is a close second. Can I test an Arduino Halloween prop without the parts? Yes. All five props on this page run in a browser simulator on the real sketch, free and with no account needed. You can set off the sensors, watch the servos and the LED strip, and change the code before you buy anything. The simulated DFPlayer shows what it plays but makes no sound. Is it safe to control a fog machine with an Arduino? It is when the Arduino never touches mains power. Wire a relay module’s COM and NO contacts across the button on the fog machine’s wired remote, leave the machine itself unmodified, and never leave it running unattended. How do talking skulls sync the jaw to the voice? Either by following the audio, turning its loudness into a jaw angle, or by a hand-timed script of cues for each line. The skull on this page uses a script, which looks crisper and works without any audio circuit. Related ## Keep going PIR Motion Sensor: How It Works, With an Arduino Arduino Relay Module: Active LOW and Startup Clicks Arduino Servo Motor with a Potentiometer Arduino Ultrasonic Sensor (HC-SR04) Tutorial Arduino Buzzer and Piezo: Beeps, Notes, Metronome Arduino Projects for Beginners, Each One Running Fog machine trigger Beginner Grabbing candy bowl Beginner Jump-scare box Intermediate Talking skull Intermediate Haunted window Intermediate The project page, with the full sketch Intermediate ## Build this for real Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed. Start building free Open the editor