A tiny, $900 wearable device being developed by an Indian billionaire entrepreneur and showcased by some of the country’s top sportspersons has sparked 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 its BrainFlow feature shows how well the brain is being supplied with blood in real time, while its Entropy feature can detect how hard the body works to shed heat.

The device can also measure thermal, immune, digestive, cognitive and emotional readings that, according to its developers, help transform how a person regulates their health.

Priced at 85,000 rupees ($907), the device comes in six colours. India’s cricket captain Shubman Gill and Olympic medal-winning badminton player P.V. Sindhu have worn it.

Some well-known doctors in the country, however, are sceptical of these claims, saying the device’s capabilities are not backed by peer-reviewed research. On prime-time television shows and 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, which has 328,000 followers, calling Temple “the biggest health scam”.

“People must be aware of wellness hacks such as wearables also, even though they are not marketed as health devices,” he told Reuters.

During a prime-time television 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.

Indian doctor Jason Philip wrote on X that assessing blood flow to the brain was not easy, and that optical signals placed over the skin at the temple would only provide data on the “superficial temporal artery”, which supplies blood to the face and skin.

In a statement to Reuters, Temple said BrainFlow and Entropy were new metrics “with emerging science”, adding that further research would follow and some metrics would eventually require 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 over Temple comes as wearable makers overseas also face questions about when a fitness feature becomes a medical one.

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 that its wrist-worn fitness tracker’s blood pressure feature appeared to be 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 had received orders from more than 62 countries since 1 November.

On its website, Temple says it is also working on detecting conditions including snoring and jaw clenching.