Heat, Noise, Motion: Using ESP32 Sensors For Strange And Useful Tricks
Once you start getting used to that sort of drift, the world feels a little less empty. You see signs of life in tiny tremors.
Aeon Flex is the writer behind Chaincoder, a blog about automation, infrastructure, and the quiet failures hiding inside modern systems. Their work focuses on how scripts reproduce bias, how abstraction erodes accountability, and why tools tend to drift toward control when nobody is watching. Chaincoder sits somewhere between technical analysis and cultural critique, written by someone who has spent too much time reading logs, reverse engineering workflows, and distrusting anything that claims to be clean, neutral, or finished.
There is something funny about the first time you stare at raw sensor output long enough that it starts feeling less likemptyemptye numbers and more like a mood. The ESP32 is small enough to lose under a pile of receipts in your car but somehow powerful enough to read a room like a tired detective with nothing left to lose. You plug in a couple of sensors and the thing becomes a little too observant. A little nosey. A little alive if you squint the right way.
I think the trick is realizing these sensors aren’t here to automate anything. Not really. They are here to tell you the things you were not paying attention to. A draft under the door. Someone pacing one floor above you. A warm body lingering a little too long behind a wall. Patterns you only notice when you force yourself to sit still and listen.
It becomes addictive. Watching the world vibrate and warm and shift in a way you never noticed with your own eyes. You stop seeing a room and start seeing signals. I guess that is the moment you become fully useless to normal people. Whatever.
Heat
Heat is slow. It feels like it carries memory. A room empties out, but the warmth takes its time leaving, like it is still deciding whether you’re worth talking to. If you’re using a cheap MLX90614 or that chunky little AMG8833 grid sensor, you’ll see how bodies smear themselves into the environment. Even with nothing fancy, even with a dumb NTC thermistor taped somewhere ugly, you get these slow bends in the temperature curve that tell you someone was here before you.
I once sat in a garage late at night with a thermal sensor logging every 50 milliseconds. It was quiet enough to hear the refrigerators two houses down cycling. At about 3 a.m. the data blipped in this soft upward curve like someone walked near the door. No footsteps. No car lights. Just a bit of heat drifting through the crack. Human trace. I checked outside and the concrete was still warm in one narrow patch where someone must have passed minutes earlier. It was weirdly intimate.
Once you start getting used to that sort of drift, the world feels a little less empty. You see signs of life in tiny tremors. People breathing. Machines sighing. Rooms changing temperature as if thinking.
Noise
If heat is the diary, sound is the confession someone mutters under their breath. You hook an I2S mic like the INMP441 into the ESP32 and suddenly the walls have a pulse. Not music. Just everything humming. A refrigerator that sounds like an old man clearing his throat. The room above you with someone dragging a chair. The hiss of old wiring when the neighbor turns on their kitchen light.
I had a mic taped behind a cheap plywood dresser in a motel in Concord for two nights. I kept noticing these faint frequency dips whenever someone walked past the doorway. Not louder. Just shaped differently. Like the air itself changed weight. Humans create turbulence even when trying to be silent. You end up recognizing the gait of strangers by how they bend the noise. A heavy step muffles the low end. A soft step flicks the high bands like a finger on glass.
After a while you can tell the difference between a person, a cat, a cheap fan, and a wall heater from the FFT alone. I don’t know if this counts as useful or just a party trick for the maladjusted. Either way, it works.
Motion
Motion sensors lie the least. They are blunt little animals. They only care that something happened. Radar doppler boards are my favorite because they see through thin materials and they do not care if the subject is pretending to be still. If a person is breathing, the radar notices. I remember pointing one at my bed while trying to see if it was sensitive enough to detect micro motion. It was. Every inhale. Every exhale. A slow wobble in the signal like a resting heartbeat. It is uncomfortable to be that detectable.
Ultrasonic sensors are different. They feel like claws scraping at the shape of the world trying to outline it. They do not just give distance. If you poll them fast enough the jitter starts telling you texture. Not precise texture. More like the difference between a still silhouette and someone shifting weight on their feet. You can even do crude hand gestures if you are patient. A little wave. A little flutter. The sensor reacts with these weird rhythmic spikes. It feels more magical than it should.
When You Combine All Three
This is where it stops being about sensors. When heat, sound, and motion overlap, the ESP32 starts forming a kind of intuition. I do not mean anything mystical. More like a primitive awareness. It knows when a room has changed even if it cannot tell you why. Maybe the radar sees stillness while the mic hears agitation. Maybe the heat rises but the motion sensor stays dead. It becomes a puzzle.
One night I had all three running in a storage unit while testing a rig. The ultrasonic readings stayed flat but the noise signature had these sharp peaks, like someone flicking a coin on a metal rail. No footsteps. No heat change. Nothing on radar. I eventually realized a bird had landed on the roof. Its weight did not reach the sensors, but the metal roof vibrated enough to give it away. That was when I realized you can detect things you cannot see or hear or feel. Machines are observant in ways humans are not built for.
The Stranger Tricks
Object memory is one of my favorites. Point a radar at a shelf and leave it for a while. The moment someone moves even a small object the wave pattern shifts. No alarms. No lasers. Just the room remembering what it used to look like and complaining when you change it.
Invisible tripwires work too. Set two ultrasonic sensors at ugly angles so their beams overlap like some crooked geometry puzzle. Anything walking through that zone distorts the wave field. There is no way to avoid a beam you do not know exists.
My favorite though might be the emotional weirdness. A person who is anxious moves in a jittery rhythm. They breathe differently. They create restless pockets of sound and air. A calm person has these slow repetitive signals. You can tell before they say a word. It feels invasive but also strangely honest. Machines notice what people hide.
The Thing That Happens After Enough Time With This Stuff
You stop reading data and start reading behavior. The sensors talk to you in their own way once you stop trying to treat them like obedient modules. Heat becomes a trail. Noise becomes a mood. Motion is whatever is left when the story breaks into movement.
You sit there watching the logs scroll and suddenly you just know that someone is on the other side of the wall. Or that a car pulled up. Or that a room you left empty now has a warm spot for no good reason. The ESP32 keeps blinking like it is bored but it sees everything.
People buy expensive security systems to get a fraction of this. You get it with a fifteen dollar board and the willingness to sit with the data until it starts whispering to you.
There is something beautiful in that. Something a little unsettling too. These circuits pay attention even when you stop.
If you want to go deeper into the strange side of ESP32 work, the guide sits here waiting, full of field tricks and the kind of ideas you never find in normal documentation.
