Miniaturised hardware and machine learning tools have brought smart wearable technologies to the masses. Modern wearable devices provide users with access to intuitive data on an unprecedented scale. While the early market was dominated by general wellness applications for the fitness enthusiast, sophisticated software is now capable of processing vast data streams and providing user-friendly output, opening a rich new vein of mobile medical technology. This relatively low-cost technology has the potential to change healthcare beyond all recognition, offering previously unimagined diagnostic, monitoring, preventative, and therapeutic options. Whilst this offers tremendous opportunities for device innovators, the blurred line between mere smart wearable devices and medical devices creates complexities, and classification as a medical device means greater regulatory scrutiny. This article provides an overview of the key considerations and discusses the increasingly dominant issues around medical device accessories, software, and smartphone applications.

What is a smart wearable?

There is no legal definition of "wearable" in the UK or EU, but the term is in common parlance mostly applied to small, mobile electronic devices with wireless communications capability. Wearables are intended to be non-invasive or minimally invasive and are worn on, or wholly or partially implanted within, the human body. The term covers a broad range of items from the very familiar watches, bracelets, and glasses, to the less common lenses, shoe inserts, patches, earbuds and even on-body robots or exoskeletons. Wearables frequently include one or more mechanical, physiological, or biochemical sensor, measuring a wide range of parameters such as gait, cardiac rhythm, and glucose.

When is a wearable a "medical device"?

Even after 31 December 2020, the regulations governing medical devices in Great Britain are based on the EU-derived legislation current at that date. The relevant EU directives on implantable medical devices (90/385/EEC) and medical devices (93/42/EEC) were given effect in UK law through the Medical Devices Regulations 2002 (UK MDR) and this legislation has so far not been amended. For the UK we therefore reference what is considered "old law" in the EU. In the UK MDR the legal definition of a "medical device" includes a range of articles, such as instruments, appliances, or materials, whether used alone or in combination, and extends to the software necessary for the article's proper application. An article becomes a medical device when it is intended by its manufacturer to be used in humans for a medical purpose. Medical purpose means the diagnosis, prevention, monitoring, treatment or alleviation of disease, injury, or disability; the investigation, replacement, or modification of the anatomy or of a physiological process; or the control of conception. The inclusion of software amongst the articles that could be medical devices means that even a generic physical device without an obvious medical purpose could be a medical device if the associated data processing, user interface or app have a medical purpose. Software is defined broadly by the EU as a set of instructions that processes input data and creates output data.

The EU Medical Devices Regulation (Regulation (EU) 2017/745, "EUMDR") which came into force on 26 May 2021 builds on the earlier definition, adding the further medical purposes of "prediction" and "prognosis" of disease. It also makes clear that software, whether embedded in a physical medical device or in a generic non-medical device (so-called "software as a medical device" or simply "SaMD"), can be a medical device in its own right. 

We await seeing whether promised new UK law on medical devices will develop the definition of medical devices in a similar way.

Where the manufacturer's intended purpose does not include a medical purpose (as provided in the definition of "medical device"), certification as a medical device is not required. Whether or not a wearable device might be a medical device will be determined from the description of the product on the labelling, in the instructions and in the promotional materials, and the operation of the device. The concept of the medical purpose means that in some cases the same physical device may be classified in different ways depending on the facts. For example, in the case of a heart rate monitor, the manufacturer's intended purpose may be merely to provide heart rate information to a wearer during exercise. On the other hand, if the manufacturer intends the device to be used for the assessment of rhythm disturbances its purpose would be the diagnosis, prevention, or monitoring of cardiac disease, and as such it would qualify as a medical device. 

In the case of software, the provision of neutral assistance with decision making, education, fitness or health monitoring, and administrative functions are excluded from being medical purposes, even when performed in a medical context. These boundaries must be navigated with care, however, as automated decision making and machine learning from a device, that affects medical decisions, diagnoses or actions (even just a referral to a physician), are likely to result in classification as a medical device.

"Used alone or in combination"

With the combined constraints of wireless bandwidth, processing power and battery consumption, most wearables are not designed to be standalone devices. They are not capable of the complex processing required to provide meaningful outputs, and they do not communicate directly to the cloud via wifi. Instead, they make use of low-power, short distance transmission protocols such as Bluetooth or near-field communication to connect with receivers, in particular smartphones. Smartphones are ubiquitous and familiar to users, have the capacity to undertake more complex processing and pre-processing of data, and can act as a gateway to the cloud for data distribution and communication with healthcare providers.

This inter-connectivity enables the sharing of functionality between wearables and their smartphone gateways but has made the regulatory boundary yet more difficult to delineate. Although smartphone hardware is generic, smartphone apps can be considered standalone medical devices if their intended purpose is medical, and even if their purpose does not meet this condition, they may fall in scope of the regulation as "accessories" to separate medical devices.

Accessories

Accessories are regulated in the same way as medical devices. An accessory to a medical device is an article that is itself not a medical device but is intended by the manufacturer to be used with a medical device to enable that device to be used in accordance with the manufacturer's intended purpose. The EUMDR introduces the additional requirement that to be an accessory it should directly assist the medical functionality of the medical device. For wearables, this means that depending on the nature of the device, smartphone, and app, the way in which they interact and how each is described by the manufacturer, each may be within the scope of the regulation. For example, even mere transfer of data from a continuous glucose monitor to a smartphone for recording and display, without further processing or manipulation, is likely to bring the software in scope as an accessory, since its purpose is to enable a medical device to fulfil its function, namely providing feedback to the user of their blood glucose level.

Products with multiple purposes

Products with multiple functions, some of which lend themselves to occasional use in a medical context, are unlikely to be considered medical devices unless a specific medical purpose is intended by the manufacturer from all the circumstances, considering the product labelling and promotional literature. General disclaimers ("this product is not a medical device") and more specific statements ("for information only" or "for research use only") will not be effective in diminishing the regulatory responsibilities of the manufacturer. One must not look at whether the manufacturer intended the device to be a medical device or not, but rather at the intended functionality of the device. If that functionality is considered as a medical purpose within the definition, then the device will be a medical device. Conversely, use of a device for a medical purpose that is not within the intended functionality of the manufacturer will not on its own make the device a medical device.

Where functions are divisible, such as software being divisible into modules, only those that serve a medical purpose will be considered medical devices. For example, cross referencing patient specific data to identify medication contraindications, interactions, and dose rates has been found to pursue a medical objective. The same software, however, when used merely to provide medical education or an electronic patient record replacing a patient's paper file, does not have a medical purpose.

Conclusion

Whether or not a wearable device is classified as a medical device is fact-specific and manufacturers must take care to consider not only their intended functionality of the physical device in determining the "intended purpose", but also the underlying algorithms and associated software even where those are embedded on generic devices or in clouds outside the wearable device. It is important to also consider whether, if not a medical device itself, the wearable might be an accessory to a medical device but assisting its functionality, and thus also subject in the EU and the UK to the same regulatory regime as a medical device. Many wearable devices might have multiple functions, only some of which would equate to the functionality of a "medical device". For this reason, we see wearable manufacturers starting out in the market with non-medical device functionality and building in the modules for medical device functionality at a later date once the original device has gained sufficient market traction to justify the significant expenditure involved in taking medical devices through the regulatory hoops to allow the manufacturer to add the CE mark or UKCA mark.