Human Factors in Connected Diagnostic Devices: Why Usability Is a Safety Question

By the Connected Diagnostics Evidence Team

Human factors are the reason a connected diagnostic device can be accurate in a lab and still fail in your home. Before trusting a result, ask whether the device was designed for someone like you, in a setting like yours — because a usability problem is a safety problem, not just a convenience issue.

Most people evaluating one of these devices ask only one question: is it accurate? That question matters, but it’s incomplete on its own. A device can meet every technical accuracy benchmark in a controlled lab and still produce a misleading result in an ordinary kitchen, at 11 p.m., held by someone who is tired, worried, or using it for the first time. This article focuses on that second, less-discussed question: can an ordinary person actually use this device the way it was designed to be used? If you’re new to this topic area generally, our Start Here guide is a good place to begin.

What Does “Human Factors” Actually Mean for a Diagnostic Device?

“Human factors” is the term device makers and regulators use for how a real person, in a real setting, actually interacts with a device. It isn’t one thing — it’s four things working together, and a weakness in any single one of them can lead to a bad result even when the device itself performs exactly as engineered.

• The user. Their eyesight, dexterity, reading level, language, prior experience with similar tools, and whether they’re calm or anxious while using it — people using a health device are often stressed, which affects how carefully they follow steps.
• The use environment. Lighting, noise, available surface space, internet or app connectivity, and whether someone is trying to use the device while also caring for a child, an older relative, or themselves.
• The device interface. Buttons, screens, alignment guides, indicator lights, and how clearly the device tells the user whether a step succeeded or needs to be repeated.
• The instructions and labeling. Whether the written or in-app instructions match what the device actually requires, and whether warnings about limitations appear where a person will see them before using the device — not buried afterward.

The FDA’s guidance on applying human factors and usability engineering to medical devices describes the goal of this work plainly: helping ensure a device is safe and effective “for the intended users, uses, and use environments,” and helping manufacturers reduce “potential use errors and resulting harm.” That guidance is written for the companies that build these devices, but the same four categories are useful for a reader trying to size up a device before relying on it.

How Does a Usability Problem Actually Happen? A Simple Process Map

Usability failures rarely happen at one single moment. They build up across a short chain of steps. Walking through that chain helps you spot where things can go wrong with a specific device you’re considering.

1. Design stage. The manufacturer decides who the device is “intended” for and what setting it’s meant to be used in. A device designed and tested mainly with trained adults in a clinic has a different intended-use profile than one meant for unsupervised home use by anyone in a household.
2. Instruction stage. The instructions translate the design into steps a person can follow. A gap here — instructions that assume steady hands, good lighting, or prior experience the reader doesn’t have — creates risk before the device is even turned on.
3. Setup stage. The person sets up the device in their actual environment, which is rarely as controlled as a lab: dim light, a shaky table, background noise, or a spotty internet connection for anything that transmits data.
4. Use stage. The person performs the actual steps — positioning, capturing, waiting, confirming. Fatigue, distraction, or unclear on-device feedback (“did that work or not?”) most often causes an error here.
5. Interpretation stage. The person, or someone reviewing the result remotely, decides what the output means. If the device or app doesn’t clearly flag a poor-quality attempt, a person may treat an unreliable result as a reliable one.

A device can be well-engineered at the design stage and still fail at the interpretation stage if nothing in the process tells the user, “this result may not be usable — try again.”

What Questions Should I Ask About Any Connected Diagnostic Device?

You don’t need an engineering background to evaluate usability. These four questions, drawn from the categories above, cover most of what matters before you rely on a device.

1. Who was this device actually tested with?

A device intended for general home use should be designed with the range of people likely to use it in mind — different ages, vision levels, and comfort with technology — not only a narrow group of confident, technically experienced users.

2. What does the instruction material assume about my setup?

Check whether the instructions describe a specific environment (quiet room, strong lighting, stable internet) as a requirement, or leave it unstated. If a requirement isn’t stated, treat that as a gap, not a green light.

3. Does the device tell me when something went wrong?

Look for built-in feedback — an on-screen message, an indicator light, or an app alert — that flags a failed or low-quality attempt. A device with no way to signal “this didn’t work” puts the entire burden of catching an error on the user.

4. Is a caregiver or second person expected to help?

Some devices assume a second set of hands — someone to hold a child still, steady a camera, or read a screen aloud. If that assumption isn’t stated anywhere, a person using the device alone may be at a disadvantage the manufacturer didn’t fully account for.

The FDA’s guidance on home-use devices makes a related point directly: home settings involve variables — like available utilities, backup power, and whether a caregiver is present — that a clinical setting controls for automatically. The agency also notes that a home user should review the instructions for use before relying on a device, and that when instructions are unclear or unavailable, contacting the device’s manufacturer or a healthcare provider is a reasonable next step.

A simple way to apply this: if you cannot confirm the instructions match your actual setup, then treat the result as unconfirmed and repeat the attempt or seek clarification before acting on it. If the device gives no clear pass/fail signal, then don’t assume a result is valid just because you completed the steps.

What Should I Do If a Device Doesn’t Perform As Expected?

Usability problems don’t always show up as an obvious error message. Sometimes the first sign is a result that seems off, a device that behaves inconsistently, or instructions that don’t match what you’re seeing on screen. The FDA’s home-use device guidance points to a few concrete steps for this situation.

• Check for a recall. The FDA maintains a public database of medical device recalls. If a device is behaving unexpectedly, checking whether it has an open recall is a reasonable first step.
• Report the problem. Unexpected device behavior can be reported to the FDA through MedWatch, the agency’s safety reporting program, at 1-800-332-1088.
• Buy from a source with a clear return policy. The FDA specifically recommends purchasing home-use devices from sources that offer clear return or exchange terms, in case a device doesn’t work as expected.
• Follow cleaning and disposal instructions. Improper cleaning or disposal can itself introduce use errors on a device’s next use.
• Keep contact information handy. The FDA recommends keeping the manufacturer’s contact information, and your healthcare provider’s, on hand in case a result or a malfunction needs follow-up.

A Printable Usability Checklist

Use this before you set up a connected diagnostic device for the first time. It’s meant to be printed or saved, not memorized.

• ☐ I have read the full instructions for use, not just the quick-start card.
• ☐ The instructions state (or I have confirmed) what environment the device needs — lighting, quiet, internet connection, or workspace.
• ☐ I know what a successful attempt looks or sounds like on this specific device, and what a failed attempt looks like.
• ☐ I know what to do if the device signals an error or a low-quality attempt — repeat the step, contact support, or stop and seek other guidance.
• ☐ If a second person is needed to help operate the device, that person is available before I start.
• ☐ I have checked whether the device has any open recalls, and I know how to report a problem if one comes up.
• ☐ I have located the manufacturer’s contact information and, if relevant, my healthcare provider’s contact information, in case a result seems unclear.
• ☐ I understand this device’s output is one piece of information, not a stand-alone diagnosis.

When Should I Stop and Get Help Right Away?

If you are experiencing a medical emergency — including severe pain, difficulty breathing, sudden severe symptoms, or anything that feels life-threatening — stop using any device and contact local emergency services immediately. No connected diagnostic device, regardless of its usability design, is a substitute for emergency care.

What This Article Does Not Cover

This guide focuses specifically on usability and human factors. It does not cover how to judge a device’s technical accuracy, how devices are regulated and cleared, or what a specific result might mean for your health — those are separate questions that deserve their own research. This article also does not evaluate, recommend, or compare any specific brand or product.

Frequently Asked Questions

Does FDA clearance mean a device is easy to use safely at home?

Clearance and usability are related but not identical. FDA guidance asks manufacturers to design for their intended users and settings, but “cleared for use” doesn’t guarantee that every person, in every home environment, will use a device correctly without reading the instructions carefully first.

What is a “use error,” and is it the user’s fault?

A use error is a mistake in operating a device that leads to a wrong or missed result. It often reflects a mismatch between the device’s design or instructions and the person actually using it, rather than carelessness alone — which is exactly why usability engineering is a manufacturer responsibility, not just a user skill issue.

Can bad lighting or a shaky hand really affect a diagnostic result?

Yes. Any device that depends on capturing an image or a precise reading can be affected by the conditions it’s used in. That’s why the use environment — lighting, stability, noise, connectivity — is treated as a core safety factor, not a minor detail.

What should I do if the instructions don’t match what I’m seeing on the device?

Stop and don’t guess. Contact the manufacturer or, if the device relates to a health concern, your healthcare provider before continuing, per FDA home-use device guidance.

Is a home-use device held to a different safety standard than a clinical one?

The underlying safety expectations are the same, but the FDA notes that home settings introduce variables — like the absence of a trained professional, inconsistent environments, and reliance on the user reading instructions correctly — that a clinical setting typically controls for automatically.

How We Verified This

The safety framework in this article — user characteristics, use environment, device interface, and instructions/labeling as the four pillars of human factors — is drawn directly from the FDA’s published guidance on applying human factors and usability engineering to medical devices, and from the FDA’s guidance on home-use device considerations.

Where a cited FDA page had moved since our sources were first identified, we located and used the current version of that same guidance rather than an outdated link. This article does not include statistics, timelines, or outcome data, because none were available from these sources for consumer-facing use — where a source didn’t answer a question, we said so rather than filling the gap with an estimate.

For more on our sourcing process, see our How We Research page.

This article is for general educational purposes only and is not medical advice. It does not diagnose any condition, recommend any product, or replace guidance from a qualified healthcare provider. See our full Medical Disclaimer for details. Connected Diagnostics Evidence is an independent editorial publication and is not affiliated with, and does not continue the operations, products, research, or institutional relationships of, any company that previously operated this domain. Last updated: September 8, 2026.