Linden by Threadcraft Labs

The room that knows itself

An air purifier that cleans your air, tracks what's in it, and shows you everything on a built-in screen. No phone needed.

Get notified In active development
Aluminum and walnut, not plastic Named for nature's air purifier Eight sensors, one purpose No cloud, no account, no tracking Repairable by design Every sensor earns its place Aluminum and walnut, not plastic Named for nature's air purifier Eight sensors, one purpose No cloud, no account, no tracking Repairable by design Every sensor earns its place

One device,
three jobs

It purifies your air. A medical-grade HEPA filter captures 99.97% of dust, pollen, smoke, and allergens. The fan speeds up when the air gets bad and quiets down when it's clean.

It monitors your environment. Built-in sensors track dust, allergens, CO2, chemicals, temperature, humidity, air pressure, and light. Each one is there because the reading actually matters to your health — not to pad a spec sheet.

It respects your privacy. No cloud account. No telemetry. Linden runs on your local network, and your data stays on the device. If we disappeared tomorrow, it would keep running.

280 millimeters of
considered design

Every surface has a job. Hover to pause, or just watch it turn.

AQI
87
PM2.5 12 · CO2 620 · 72°F
E-ink display
Top exhaust
Walnut accent
HEPA filter access

Built from things
that age well

Chosen to age well, not to hit a price point.

Natural walnut

Hand-finished crown and accent panels. Every unit looks slightly different because real wood does.

Matte aluminum

Machined and anodized enclosure. Conducts heat away from electronics. Doesn't yellow, crack, or creak.

AQI 87
Always on. No backlight. Reads like paper.

E-paper display

3.7-inch e-ink screen. Readable in direct sunlight. Zero power draw between refreshes.

Eight things worth knowing
about your room

Sensirion and Bosch sensors. Calibrated on-device.

PM2.5
0 ug/m3
Fine particles from cooking, candles, wildfire smoke. The number your lungs care about most.
CO2
0 ppm
Rises when people are in the room. Above 1000 and you'll feel foggy. A window usually fixes it.
VOC Index
0
Invisible chemicals from cleaning sprays, paint, and new furniture. The stuff you stop noticing but your body doesn't.
Temperature
0 °F
Tracks drift over hours and days. Useful for spotting HVAC problems before they're obvious.
Humidity
0 %
Below 30% and your skin dries out. Above 60% and mold starts growing.
PM10
0 ug/m3
Bigger particles like dust, pollen, and pet hair. What makes you sneeze.
Pressure
0 hPa
Changes mean weather is coming. Also helps the other sensors give you more accurate readings.
Light
0 lux
How bright the room is. Helps Linden know when you've gone to bed and when the room is empty.

Glanceable from
across the room

Your air quality, sensor readings, and system status — always visible, no phone required.

It looks like paper behind aluminum. Because it basically is.

Always on, always readable. Updates every 30 seconds. Uses zero power between refreshes.
AQI
87
PM2.5
12 ug/m3
CO2
620 ppm
Temp
72°F
Humidity
45%
VOC
Low
Pressure
1013
linden.local

No account. No cloud.
No tracking.

Most air purifiers need an account, an app, and send your data to the cloud. Linden doesn't. Your data stays on the device. Export it anytime if you want it.

Works with Home Assistant and other smart home systems. No vendor lock-in.
Your data stays here
Sensor readingsLocal only
Historical dataOn-device SQLite
Web interfacelinden.local
Home AssistantLocal MQTT
Data exportCSV / JSON
0 bytes sent to the cloud

Proof that it's working

The device pulls outdoor air quality data from the EPA every hour and compares it to what's inside your home.

When wildfire smoke pushes outdoor PM2.5 to 80 and your indoor reading is 8, you can see exactly what the filter is doing for you.

Indoor
8
PM2.5 ug/m3
vs
Outdoor
42
PM2.5 ug/m3

Wake up knowing
how you slept

Every morning, the e-ink display shows overnight CO2 levels — average, peak, and a ventilation grade. High CO2 in bedrooms causes cognitive fog and poor sleep. Linden tracks it so you don't have to guess.

High CO2 in a closed bedroom makes you feel groggy in the morning. Most bedrooms hit unhealthy levels by midnight with the door closed.
Sleep Report
GOOD
Avg CO2 623 ppm
Peak CO2 812 ppm
>1000 ppm 0 min
Ventilation was good

It knows when
you're cooking

When PM2.5 and VOC both spike — the signature of frying, sauteing, or toasting — the fan automatically boosts to clear the air faster. No manual turbo button. It settles back down on its own when the air clears.

It's smart about it — a candle or perfume spray won't trigger boost mode. It takes both smoke particles and cooking gases together to activate.
Air quality monitor Normal
PM2.5 18 ug/m3
VOC Index 92
Normal
Fan: Auto

Schedules itself,
adapts in real time

Set fan schedules by time of day — quiet at night, responsive during the day. The device follows your routine and adapts to what the sensors are reading.

Time-based schedules, sensor-triggered responses, and smart home integration work together without requiring any manual intervention.

Works with Home Assistant out of the box. Full data export whenever you want it.
7:00 AM Morning Auto
6:32 PM Cooking detected Boost
10:00 PM Night Sleep
7:00 AM Sleep report Good

Designed, assembled, and tested by hand

We design the enclosure, source the components, assemble the boards, and test every unit ourselves.

When something can be replaced, repaired, or upgraded, we design for that. The HEPA filter slides out with a magnetic panel. The software updates over your local network.

Designed in Wisconsin
Walnut
Aluminum
HEPA H13

Named for nature's
air purifier

The American linden — called basswood in Wisconsin, where we build Linden — is one of the most common trees in the state's forests. Scientists use its broad, heart-shaped leaves to measure urban air quality because they capture particulate matter with remarkable efficiency.

For centuries before that, communities gathered under linden trees to hold court, because tradition held that no one could tell a lie in its shade. Its wood is the choice of master carvers — prized for its fine grain and the way it responds to skilled hands.

We thought all of that sounded like a good name for something you trust with the air your family breathes.

Honest air.
Linden leaf

Specifications

The full list.

Dimensions
280 × 180 × 180 mm vertical tower
Weight
2.5 – 3.5 kg assembled
Materials
Matte anodized aluminum, natural walnut accent
Filter
HEPA H13, tool-free magnetic replacement
Display
3.7" e-paper, 480×280, 4-level grayscale
Compute
Custom computer module with plenty of storage for years of data
Connectivity
WiFi and Bluetooth
Interface
Built-in web dashboard at linden.local
Fan
Whisper-quiet fan with three speed profiles
Power
Single power cord. That's it.
Software
Custom software, works with Home Assistant
Cloud
None. Your data never leaves your home.

Built in the open

Linden is in active development. We'll email you when prototypes are ready.

Email notifications aren't wired up yet — we're building in the open. Check back soon.

Fresh air!