Slate

Heat illness is predictable. Nobody on the crew is watching for it.

The client had a validated model for heat strain built on skin temperature, heart rate and work intensity. What they did not have was a device a crew would wear. Consumer smartwatches died in a week on site, and the clip-on industrial monitors they trialled ended up in lunchboxes by the second day.

The brief was a wrist device that a supervisor could hand out at the start of a shift, that would warn the wearer and the supervisor before a problem, and that would still be working at the end of the season.

Spent a week on roofs before we drew anything.

Field research changed the product more than anything that came after it. Crews took gloves off to use touchscreens, so there is no touchscreen. They could not hear a beep over a compressor, so the alert is a strong haptic pattern plus a light bar that reads from across a site. They wore it over a sleeve as often as under one, so the strap adjusts over a wide range and the sensor pod is sprung to keep contact.

Industrial design and mechanical engineering ran as one workstream. The housing is a two-shot moulding, hard shell over a soft skin, with the optical sensor window and the charging contacts sealed as a single insert. There are no exposed fasteners and nothing for grit to get behind. We went through three rounds of appearance models worn by real crews before the shape settled.

Electrically, the constraint was a full shift plus margin between charges with continuous optical heart rate, which is unforgiving. We tuned the sampling schedule to work intensity, so the sensor runs harder when the wearer does and rests when they do. The radio talks to a supervisor's phone and to a small site gateway for crews out of phone range.

Formative usability studies ran with crews in Texas and Arizona in July. Summative validation confirmed that first-time users could interpret every alert correctly without a briefing. Design transfer went to a wearables manufacturer with experience in two-shot moulding and sealed optical assemblies.

• The light bar is visible in direct sun at thirty metres. We measured it on a roof in August, which is the only test that counts.
• Charging is a five-unit dock that lives in the truck. Nobody takes a charger home, so the product does not depend on it.
• The strap uses a hook-and-loop closure over a silicone core. Buckles broke, pin-and-tuck straps did not fit over sleeves, and magnets picked up swarf.
• The device has one button and it does one thing: acknowledge. Everything else is automatic.
• Every unit logs to local memory for thirty days, so a supervisor can reconstruct a shift even if the phone was never in range.

Slate is shipping to the client's first commercial customers. The second colourway is in tooling, and the client's in-house team now owns the firmware, with our test rig on their bench.