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SensingDesign complete (stages 1–6, rev B), not built, not validated

CoolerCheck

Walk-in cooler and freezer faults found before the food is lost

Tells a kitchen and its refrigeration contractor what is going wrong with a walk-in (door open, failed or stuck defrost, short-cycling, compressor trouble, power loss) early enough that the fix is a daytime visit instead of a dumpster of food.

Who buys it
The refrigeration contractor, who resells, installs and watches a fleet dashboard; the user is the independent restaurant.
Why it pays
Expected walk-in trouble cost for a cooler + freezer site falls from about $1,617/yr with no monitoring (or $915/yr with a $149 threshold alarm) to about $376/yr (est., failure rates unverified). The contractor earns about $12k/yr gross margin per 45 sites (est.).
Target price
$199 site kit (gateway + 2 pucks) + $39 per CT node + $12/site/month, contractor wholesale (target)
First-minute wow
Every alert names a fault class with a suggested cause (for example "suspected defrost failure") and a 24 h chart, instead of a bare temperature number.
See the CAD designConcept page
CoolerCheck concept: the idea and where each part goes
The concept. The CAD design is below, under Printable CAD.

What the research found

And how this design answers it

  • Temperature sensors are a commodity → every alert is a named fault class with a suggested cause, sold through contractors bundled with their service
  • Contractor resale is unproven → white-label fleet dashboard, evidence charts they can bill from, IEMI handles billing
  • Defrost causes false alarms → product probe in a glycol bottle drives alerts; the cloud learns the defrost schedule and the CT node confirms compressor off
  • Radio through a steel walk-in → electronics outside the box, probes through the door gasket, 915 MHz LoRa to the gateway, LTE-M backhaul
  • Batteries sag in the cold and bake on the roof → puck battery stays at kitchen temperature; CT node uses a −60…+85 °C Li-SOCl₂ cell in white ASA

Use case

Failed defrost at 2 am

OwnerKitchen managerRefrigeration technicianCoolerCheck cloud

  1. 01Trigger: the freezer's 02:00 defrost timer fails and ice builds on the coil
  2. 02Detection: the cloud sees no defrost in the learned window, then a second miss at 08:00, with the cycle minimum creeping up and compressor duty up 34%
  3. 03Alert: the technician gets a P2 ticket "suspected defrost failure" with a 24 h chart; the owner gets "Freezer OK for now, contractor notified"
  4. 04Action: the technician books a 10:00 visit at the normal rate, defrosts the coil and replaces the timer

Outcome: No product lost; about $4,800 of stock and a $158 emergency premium avoided (est.)

How it works

Architecture

  1. 01

    Sense: two DS18B20 probes (air + glycol product) and a door reed on a puck outside the box; optional CT clamp node on the condensing unit

  2. 02

    Send: 915 MHz LoRa (AES-128-CTR + CMAC) to a gateway in the office, then MQTT over TLS on LTE-M

  3. 03

    Decide: cloud learns each box's defrost schedule, duty and starts/h, then runs rules R1–R10

  4. 04

    Tell: SMS, voice, push and email by escalation ladder; white-label contractor dashboard and owner app with temperature logs

Hardware

Real parts, buyable today

Bill of materials: about $49 per puck, $46–51 per CT node and $91 per gateway at qty 1–10; about $22 / $35 / $62 at 500 pcs (est.).

BlockPartWhy this part
Radio + MCU (all three devices)RAK3172 (STM32WLE5 + SX126x)One radio part everywhere keeps cost and firmware simple; LoRa reaches the office through kitchen walls
Puck power2× Energizer L91 + TPS610994 boostAbout 1.6 mAh/day; battery stays outside the cold box
CT node powerSaft LS14500 Li-SOCl₂ + TPS7A0230 LDORated −60…+85 °C for a rooftop condensing unit
GatewayESP32-S3-WROOM-1 + Quectel BG95-M3 LTE-MNo restaurant Wi-Fi needed
Gateway backupBQ24074 power path + 18650Keeps reporting for at least 24 h through a power cut and detects mains loss

Mechanical

Printable CAD

13 parts, generated from code and checked as closed solids. Pick a part to inspect it, or download the STL files to print.

See the CAD parts render
CoolerCheck printable parts, rendered from the CAD
Render of the printable parts from the actual CAD. Not yet printed or photographed.

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Open risks we are working on

  • Contractor resale is unproven: kill if fewer than 3 of 10 contractors commit to a paid pilot
  • Price pressure from $55–149 no-fee sensors; above about $30/month retail the owner buys a Temp Stick
  • Defrost false-alarm target (< 1 per box per week after day 7) is unproven on demand-defrost controls
  • Puck antenna next to a steel door frame will detune and must be tuned on a real frame
  • Savings rest on unverified failure rates; thresholds are hypotheses until pilot data
  • FCC classification of BW500 LoRa as DTS and certification cost ($5–15k est.) not yet confirmed

Design stage only: nothing on this page is for sale. Specifications and prices are targets.