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

ColdChain Guard

A reusable reefer logger that hands the receiver the trip record at the dock

Stays in the reefer box for years, records every trip by itself (product-simulant and air temperature, door openings, route), warns the driver while the load can still be saved, and gives the receiver a read-only trip record by QR code.

Who buys it: The owner of a 1–20 truck reefer fleet or a small food distributor running its own box trucks and vans, not the large shipper.
Why it pays: Replaces $20–31 single-use USB loggers per load, about $4,160–6,450 a year per truck at 4 loads a week (est.). One disputed or rejected load ($3,000–8,000, est.) costs more than five years of the service.
Target price: $249 kit (logger, door tag, 2 probes) + $9/truck/month including data (target)
First-minute wow: At the dock the receiver scans the QR code on the logger and sees the whole trip chart, with door openings marked, before signing the bill of lading.

See the CAD design Concept page

ColdChain Guard 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

Tive, Sensitech and Emerson own per-shipment cargo tracking → sold per truck to small carriers; the logger stays bolted in the box and the trip is the record
Single-use loggers cost only $20–31 → cheaper than a USB logger per load after about 7 weeks, with live warnings and no PC or cradle
Camera and 'AI' added cost and no value → camera deleted; plain rate-of-rise and defrost-aware rules that a driver can read in one SMS
Door openings cause air-spike false alarms → product probe in a glycol vial drives alerts, and a BLE door tag labels every opening
Radio can't get out of a closed aluminium box → 120 days stored on the device, upload at every door opening, optional external antenna through the door seal
Batteries fail in the cold → primary Li-SOCl₂ C cell, about 2 years per $12 swap, PA12 and TPU parts for −30 °C

Use case

Yogurt load about to be refused at the dock

Owner-operatorGrocery DC receiverBrokerColdChain Guard cloud

01Trigger: the receiver probes the top pallet layer by the door at 41 °F against a 33–38 °F spec
02Evidence: the driver points to the QR code; the trip page shows the product simulant at 35.8–37.4 °F for 11 h with two door events
03Decision: the receiver re-probes the pallet core, reads 37 °F and accepts; the broker gets the trip PDF
04Record: the trip is closed with a hash-chained record and kept for 13 months

Outcome: About $5,000 load kept and no claim filed (est.)

How it works

Architecture

01
Sense: 2 TMP117 probes (glycol vial + air), SHT45 inside, LIS2DH12 motion, BLE door tag with a Hall switch
02
Decide: trip state machine, limit and rate-of-rise rules run on the device so they work with no signal
03
Send: MQTT over TLS on LTE-M (nRF9151) hourly and at every door opening, with 120 days of store and forward
04
Tell: SMS to the driver and owner, fleet dashboard, receiver trip page by QR, 12-month CSV/PDF archive

Hardware

Real parts, buyable today

Bill of materials: about $168 per kit at qty-1 prices, about $120 at qty 100 (est.).

Block	Part	Why this part
Cellular + GNSS + MCU	Nordic nRF9151-LACA-R7 SiP	LTE-M with PSM and GNSS in one part, $22.69 at qty 1
BLE	Raytac MDBT42Q (nRF52832)	Talks to the door tag without a cable across the hinge
Product probes	2× TI TMP117 in 6 mm stainless tubes	±0.1 °C class digital probes on one I²C bus
Power	Saft LS26500 Li-SOCl₂ C cell + supercap	Works to −30 °C, about 2 years per cell, nothing for the driver to charge
Door tag	nRF52832 + TI DRV5032 Hall switch + LS14250	Solid-state door sensing, more than 5 years per cell

Mechanical

Printable CAD

9 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

ColdChain Guard printable parts, rendered from the CAD — Render of the printable parts from the actual CAD. Not yet printed or photographed.

Loading the CAD…

Real CAD · drag to rotate · scroll to zoomReal CAD · swipe sideways

Open risks we are working on

LTE-M may not get out of a closed insulated box; live alerts then depend on door openings or the external antenna kit (bench test T7)
Small carriers are price-sensitive and hard to reach; the channel (brokers, reefer dealers, load boards) is untested
Receivers may not accept a carrier-owned record over their own probe reading; it is evidence, not a verdict
Li-SOCl₂ pulse behaviour at −25 °C with LTE peaks needs the supercap sizing proven (T8)
Kit margin is thin at low volume; the business depends on subscription retention

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