Prevayl Innovations Limited v Whoop Inc

This dispute came from the wearable technology market. Prevayl owned a UK patent for a bra that measured biosignals from the wearer. The court described it as a smart bra. The patent was not about inventing biosignal measurement from scratch. That general concept was already known.

The claimed advance was narrower. Prevayl said the invention improved comfort and appearance by locating the relevant sensing hardware in a side region of the bra rather than in more prominent positions. The patent also referred to avoiding placement in the underband.

Whoop supplied a sports bra with a pocket for a wearable sensor module. It also supplied the Whoop 4.0 module, usually through a membership model and more commonly worn on a wrist strap. Prevayl said Whoop's products infringed. Whoop replied that the patent should be revoked because it was not new or inventive over earlier publications.

That left the court with the usual patent fight in three parts. First, what exactly did the claims mean? Secondly, were those claims valid? Thirdly, if they were valid, did Whoop infringe by supplying the bra, the module, or both?

The first issue was claim construction. In patent cases, wording matters. The court had to decide what the patent required when it referred to a measuring apparatus, a sensor assembly, side regions and the underband.

The judge held that the patent claims required all of the sensor assembly, meaning the entirety of the one or more sensors used, to be in one side region and not in the underband. The judge rejected the view that the claim also required the electronics module to be in that side region. On the wording of claim 1, the electronics module could be elsewhere on the bra.

The court also considered claim 2, which added a pocket in the side region. The judge read that claim as not requiring the sensor assembly itself to be in the pocket. The description pointed more naturally to the pocket being for the electronics module, with the sensors and module being close to each other in the side region.

Once the claims were construed, the court turned to validity. Whoop relied on two earlier patent publications from November 2018. One was a US patent application directed to a wearable monitoring device in fabrics, including a bra example. The other was a PCT application about a bra for measuring a physiological signal.

Finally, the court had to consider indirect infringement under section 60(2) of the Patents Act 1977. That issue mattered because Whoop supplied the bra and the module separately. Whoop accepted that the Whoop Bra with a Whoop 4.0 installed would fall within the claims, and it did not dispute that supplying the bra would be an infringing act if the patent were valid. The real argument was about the separate module.

Prevayl survived the novelty attack based on the US publication, but only just. The earlier document disclosed a bra embodiment with sensors in various possible locations, including positions in a side region and not in the underband. It also referred to using at least one sensor.

That was not enough to destroy novelty. The judge said the earlier document did not give clear and unmistakable directions to use a single sensor located in a side region and not in the underband. It disclosed that arrangement only as one among many possibilities, without singling it out. So claim 1 was not anticipated by that document, and claim 2 was not either.

Prevayl then lost on inventive step. Starting from the US publication, the judge found that the skilled team would have seen using one sensor as an option already taught by the document. The next question was where to put it. The evidence showed that there were known disadvantages in placing sensors or related hardware at the front or back, including discomfort and appearance issues. That made the side region an attractive alternative.

Prevayl argued there was a market or technical mindset that sensors had to be at the front or back, or if at the side then in the underband. The judge did not accept that. The evidence showed there were sound design reasons for using the underband, especially because hard components sit more easily in a stiff part of the bra. But the judge found that placing the sensors in the side region outside the underband was still an obvious workable option.

The court also held that claim 2, which added a pocket in the side region, was obvious. The evidence accepted by the judge was that a pocket for a removable electronic item was a known design option available to the skilled bra designer. If needed, a mesh pocket was also within common general knowledge.

Whoop also succeeded on inventive step over the PCT publication. Although that document dealt with a conventional bra rather than a sports bra, the judge held it would still have been obvious to apply the side-placement idea in a sports bra by adding an underband or otherwise adapting the concept. The evidence, taken together, supported the conclusion that a skilled team would have found it obvious to make a sports bra with sensors in the side region and not in the underband.

The result was that both claims 1 and 2 were invalid for lack of inventive step.

Even though the patent was invalid, the judge still decided what would have happened on infringement if the patent had been valid. That part of the judgment is commercially useful for businesses that sell systems, accessories and compatible hardware.

Whoop supplied two separate products. The first was the Whoop Bra, which had a pocket for a wearable sensor module. The second was the Whoop 4.0 module. The module did not have to be used with the bra and was more commonly worn on a wrist strap. There were also alternative suppliers of modules that would fit and work in the Whoop Bra.

Whoop accepted that the Whoop Bra with a Whoop 4.0 installed would fall within claims 1 and 2. It also did not dispute that supplying the Whoop Bra would be an infringing act if the patent were valid. The contested point was narrower: whether supplying the separate Whoop 4.0 module could itself amount to indirect infringement under section 60(2).

The judge reviewed earlier authorities and summarised the section 60(2) test in practical terms. There is indirect infringement where, on the balance of probabilities, a person supplies in the UK a means relating to an essential element of the invention, adaptation or use of that means with other means would put the invention into effect, and the supplier knows or it is obvious that at least some ultimate users will use it that way in the UK.

Applying that test, the judge rejected Whoop's argument that the module was not tied closely enough to the technical teaching of the invention. The court said the invention as claimed was a bra including a measuring apparatus with a sensor assembly. The measuring apparatus was not a completely subordinate part of the invention. It was central to the promised advantage of a comfortable and sightly bra that would measure biosignals.

The judge also noted that it was not disputed that, when used with a Whoop Bra, the Whoop 4.0 would put the invention into effect. Nor was it disputed that it was foreseeable that some users would do exactly that. On that basis, the judge held that supply of the Whoop 4.0 module would have constituted infringement if the patent had been valid.

The court also said there was no objection in principle to more than one type of supplied means amounting to indirect infringement of the same patent. In other words, a business may face exposure through the main product and through a separate compatible component.

This case is especially relevant if your business improves products by rearranging known components rather than inventing a new sensor, chip or material. That is common in consumer technology, sports products and wearables. A better location can improve comfort, appearance, washability and usability. Those are real commercial gains. But they do not automatically create a strong patent.

The judge looked for a convincing reason why the skilled team would not have seen the side region as an obvious place to try. Prevayl could point to design challenges and to the fact that many products used other placements. That was not enough. The court wanted evidence that side placement outside the underband would have been dismissed as a workable option at the priority date. That evidence was missing.

For founders and product teams, the practical message is to build the patent story early. If your invention is about placement, housing, interface or configuration, keep records showing the technical trade-offs, failed alternatives and reasons the final arrangement was not routine. If the answer is simply that it was more comfortable or looked better and the side was an obvious place to move things, the patent may be vulnerable.

The case also matters for businesses with modular products or accessory ecosystems. Patent risk does not stop with the finished item. If customers combine your module with another product in a way that puts a patented invention into effect, your supply model may still be challenged. Product design, compatibility, instructions and marketing all matter.

If you are building a wearable or connected product, this judgment points to a practical review list. Patent disputes often turn on ordinary business documents and product decisions, not just the final claim wording.

For your own patent position, review design notebooks, prototype notes, testing records and internal discussions showing why a particular placement or arrangement was chosen. If there were comfort, signal quality, washability or manufacturing issues, record them clearly. Evidence of real technical difficulty can matter.

For infringement risk, review the whole customer journey. Look at how the product is sold, what parts are supplied separately, what combinations are encouraged, and what your marketing suggests customers should do. A separate module may still be relevant if it helps users complete the patented combination.

Also review compatibility claims. If your product is designed to fit, work with or be inserted into another item, that can become important in an indirect infringement analysis. The legal question is not only what the component does on its own, but whether its intended use with other means would put the invention into effect.

The patent had an unchallenged priority date of 9 September 2019. The case was heard on 20 and 21 January 2025. Judgment was handed down on 27 February 2025 in the Intellectual Property Enterprise Court.

The overall result was that the patent was invalid for lack of inventive step. The court nevertheless gave a hypothetical infringement ruling, stating that if the patent had been valid, supply of either the Whoop Bra or the Whoop 4.0 module would have infringed.