A tiny, $900 wearable device developed by an Indian billionaire entrepreneur and showcased by some of India's top sportspersons has drawn criticism from doctors who say its claims of tracking blood flow to the brain are exaggerated. The Temple device is less than 1 inch (2.54 cm) wide and weighs under 2 grams (0.07 oz). It sticks to the side of the head between the forehead and the ear, or the temple area. Promotional materials for the device, developed by Deepinder Goyal, say that its BrainFlow feature shows how well the brain ​is being supplied with blood in real time, and its Entropy feature can detect how hard the body works to shed ​heat. Read: Smartphones are revolutionising medicine It can also measure thermal, immune, digestive, cognitive and emotional readings that help to transform how a person ⁠regulates their health, they say. Deepinder Goyal's Rs 85,000 wearable faces questions over scientific claims | Deepinder Goyal, co-founder of Zomato, has launched a wearable startup called Temple that has run into a public scientific credibility test. Doctors are questioning the evidence behind its ₹85,000… pic.twitter.com/cBGS89Y3Ft — Economic Times (@EconomicTimes) November 9, 2026 Priced at 85,000 rupees ($907), the device comes in six colours. India's cricket captain Shubman Gill and Olympic medal-winning badminton ​player PV Sindhu have worn it. Some well-known doctors in the country, however, are sceptical of the claims, saying peer-reviewed research does not back the device's capabilities. In prime-time shows and on social media, they are calling for the device to come under the purview of medical regulators. Prominent Indian hepatologist Cyriac Philips, known as "TheLiverDoc", has been criticising the device on his X account with 328,000 followers, calling Temple "the biggest health scam". The Liver Doc goes another round with Deepinder Goyal | Hepatologist and social media personality Cyriac Abby Philips, popularly known as ‘The Liver Doc,’ has again challenged Zomato founder Deepinder Goyal, alleging his wearable device Temple was nothing but a “beautiful scam.”… pic.twitter.com/8o0kCngdJ8 — Economic Times (@EconomicTimes) November 10, 2026 "People must be aware of wellness hacks such ​as wearables also, even though they are not marketed as health devices," he told Reuters. On one prime-time TV discussion, paediatrician and nephrologist Sanjeev ​Bagai called Temple a "gimmick", saying it had "no formal approval or clearance". Goyal has hit back at the criticism from doctors, saying Temple is a "fitness tracker and wellness ‌device", not ⁠a medical one. Temple is an ambitious project. The team is delusional enough to think we can build this. And we will. Here's what we are building. Join the ride. https://t.co/sZugOhdb2f pic.twitter.com/fPZSISAr6V — Deepinder Goyal (@deepigoyal) November 6, 2026 Indian doctor Jason Philip wrote on X that assessing blood flow to the brain was not easy, and optical signals placed over the temple skin would only give data on the "superficial temporal artery" that supplies blood to the face and skin. Temple's core pitch collapses under basic medical scrutiny. It is sold as an adhesive optical sensor placed over the temple of the head, that gives a measure of the blood flow of the brain. And a laughable gravity ageing hypothesis. Blood flow to the brain is by the… pic.twitter.com/C5pfoWRTKT — Dr Jason Philip. M.S., MCh (@Jasonphilip8) November 6, 2026 In a statement to Reuters, Temple said BrainFlow and Entropy were new metrics "with emerging science", and that more research would follow, adding that some metrics would eventually need regulatory ​approval. India's health ministry did not respond ​to Reuters queries, and the ⁠government has so far not reacted to the public debate. Scrutiny on wearables makers The debate on Temple comes as wearable makers overseas also face questions on when a fitness feature becomes a medical one. Read More: Your fitness tracker is 27% to 93% inaccurate: Stanford Some Apple Watch ​features, such as hypertension notifications, have received US Food and Drug Administration clearance as software-based medical features. Last ​year, the US ⁠FDA warned Whoop, saying its wrist-worn fitness tracker's blood-pressure feature looked like a medical one — a view the company disputes. Goyal is best known for co-founding Eternal, which houses India's biggest listed food-delivery company, Zomato and has a market value of about $35 billion. The 43-year-old stepped down as chief executive of Eternal ⁠this year ​to focus on Temple. Temple, which has professors from the University of Ottawa and Harvard ​on its advisory board, raised $54 million in February at a valuation of about $190 million. Goyal said Temple has received orders from more than 62 countries since November 1. On its website, ​Temple says it is also working on detecting conditions including snoring and jaw clenching.