Zomato and Eternal founder Deepinder Goyal has hit back at doctors who have questioned his new health wearable Temple, insisting in an open letter that the device is not a scam and that he has staked his own money and reputation on getting the science right.
The sharp exchange, played out on social media on 5 November, has turned one of India's most talked-about gadget launches into a public argument between a celebrated entrepreneur and some of the country's most vocal medical voices.
Goyal addressed his post on X to "Dear Concerned Indian Doctors", responding to criticism from physicians who say the Rs 85,000 head-worn device makes claims about measuring blood flow inside the brain that its hardware cannot support. He laid out seven points in defence of Temple, ending with a line that has since been quoted widely: "Hope this addresses some or all of your concerns. If not, keep raging."
Temple is Goyal's first major venture since stepping away from the chief executive's role at Eternal, the company behind Zomato and Blinkit. With pre-orders open and deliveries promised within three months, the questions being asked by doctors go to the heart of what the device can actually do.
What Temple claims to do
Temple is a small, pill-shaped wearable worn on the side of the head, held in place by a disposable medical-grade adhesive grip. Unlike wrist-based trackers, it uses light-based optical sensors positioned at the temple to track what the company calls BrainFlow — cerebral blood flow and oxygenation in real time.
The device also calculates a biological entropy score, a number between 1 and 250 meant to indicate how much physiological strain the body is under from factors such as stress, poor sleep and caffeine intake. Goyal has claimed in posts on X that Temple is the most accurate heart-rate tracker compared with all flagship wearables, even during intense exercise in heart-rate zones four and five.
The device is priced at Rs 85,000 and comes in six colours. Pre-orders opened on 1 November through the Temple website and app, with deliveries promised within around three months. The product is marketed strictly for general wellness and research. It is not a medical device, and it has not been approved by medical regulatory bodies.
Temple is being developed under Goyal's longevity project Continue Research. At its core is an idea he has called the Gravity Ageing Hypothesis — the proposition that ageing is primarily driven by a lifelong, cumulative deficit in cerebral blood flow, which he attributes to the effect of Earth's gravity. It is a bold claim, and it is the claim that has drawn the sharpest scrutiny from the medical community.
Goyal's seven-point defence
In his open letter, Goyal began with what he called a business lesson. If Temple were a scam, he argued, and any of what the company said was untrue, users would find out within days of wearing it. The device comes with a 14-day, no-questions-asked return policy — something he pointed out that even Apple does not offer in India. "If the product doesn't work, it fails out of the gate and the company dies before recovering a tenth of its R&D," he wrote.
His second point was about money. Goyal said the team has already spent 30 million dollars building Temple, 20 million dollars of which is his own money. Selling a few thousand devices, he argued, would recover only a small fraction of that investment. "A scam that pays nothing is not a scam anyone would run," he wrote.
Third, he said he left the chief executive's role at Eternal to chase purpose with Temple, and that the venture is not about money. "I have enough of it to last for generations," he wrote. "I am not staking a reputation earned over 20 years on making a quick buck." Fourth, he pointed to the company's funding: employees bought into a round a few months ago, and the round now being raised is mostly made up of customers. "Scams don't build that cap table," he wrote.
Fifth, he addressed the absence of peer-reviewed evidence. Most wearable companies start with internal studies, he argued, noting that Whoop shipped its band in 2015 and the first published validation followed a few years later. Temple, he said, holds itself to a higher standard, and pre-prints are on their way.
Sixth, he said there comes a point when a company has to stand behind its work: "we believe in our science, and the product is now valuable enough for people to pay for and use." Finally, he expressed confidence that the team is building something the world will be "positively astonished" by, adding that independent studies will emerge once the device is in people's hands.
He closed by teasing that the most groundbreaking features in Temple have not even been made public yet — "and some of them, thankfully, have nothing to do with doctors."
Goyal has also been careful to define what Temple is not. "Temple is a fitness tracker, and wellness device. We are not a medical device," he wrote in a separate post. "If at some point, we clinically validate any of our metrics, we will let you know."
The doctors' case
The sharpest response came from hepatologist Dr Cyriac Abby Philips, widely known online as The LiverDoc. In a lengthy post on X, he said flatly that "there is no science" behind the device, and went further, calling it "science fraud" and a scam. He argued that Goyal had provided no real evidence that a device sitting on the superficial temporal artery could measure and interpret blood flow inside the brain.
The anatomical point is central to the criticism. The superficial temporal artery is an extracranial blood vessel — it lies entirely outside the skull and supplies blood to the side of the face, the temple and the scalp. Readings taken from that area are heavily influenced by the scalp, skin and muscle tissue, critics say, making it highly questionable whether the device can measure true blood flow inside the brain at all.
In his post, Philips wrote that the device can only measure blood flow and flushing to the face in humans and has "absolutely NOTHING to do with the brain as they claim".
Philips also said that Temple's own science lead, Avi Roy, has accepted that the device is not yet proven to measure brain flow or the entropy score claimed on the company website, and has addressed concerns about poor methodology and statistical misrepresentation without responding to what Philips described as clear evidence of data falsification in the company's pre-print papers.
He contrasted Temple with Whoop, the company Goyal himself had cited, saying Whoop measured and validated exactly what its wearable can measure, within the limits of human anatomy and physiology. He added that Goyal has blocked him on X.
Another voice in the debate, gastroenterologist Dr Zubin Sharma, thanked Goyal for what he described as an admission that Temple is shipping with no research at clinical-outcome or peer-reviewed level. He also questioned the priorities behind the project, suggesting the money spent could have been directed at healthcare problems India actually faces.
Medical experts more broadly note that Temple's claims rest on internal studies with very small sample sizes rather than peer-reviewed, independent trials.
A launch under the spotlight
Temple has been one of the most discussed gadget launches in India in recent weeks, with Goyal himself sharing regular updates about it on X. Indian cricketer Shubman Gill was recently spotted wearing the device during a practice session, adding to the buzz around it.
For Goyal, the stakes are personal as well as commercial. He has framed Temple as a purpose-driven project, the reason he stepped away from running one of India's largest consumer internet companies. In his letter, he was explicit that he is staking a reputation built over two decades on the venture.
For the doctors, the stakes are different but no less real. Their concern is that a device priced at Rs 85,000, marketed with claims about the brain, could mislead buyers about what it can do, particularly when the underlying science has not been published or independently checked.
What happens next
The immediate test will be the pre-prints Goyal has promised. If the company publishes detailed research that independent scientists can examine, the debate will move from social media to the scientific literature. If the papers do not arrive, or fail to convince, the criticism is unlikely to fade.
The first deliveries, expected within three months of the 1 November pre-order opening, will also matter. Early users will quickly form their own views on whether the device does what it promises, and Goyal himself has argued that this is the ultimate test — a product that does not work, he said, would fail within days of use. For now, the argument continues in public, with neither side showing any sign of softening.
(Reporting based on NDTV, NDTV Profit and The Times of India.)