Zomato founder Deepinder Goyal has created a new wearable device called ‘Temple’, which promises to monitor physiological signals and give insights into the brain’s blood flow.
The Temple is a small headpiece that attaches to the skin between the forehead and the ear. It is less than 1 inch (2.54 cm) wide and weighs under 2 grams (0.07 oz), and costs around Rs. 85,000.
Several medical professionals have expressed their concern over whether evidence is available behind the device’s functionality, while Goyal has continued to defend the science behind his wearable.
The wearable has been promoted by several influential sportspersons in India, including Cricketer Shubman Gill and Badminton Player P. V. Sindhu.
The company claims that the wearable is beyond anything a regular fitness tracker can do. The wearable tracks:
Brain Flow: A unique metric that allows users to track changes in blood flow to the brain in real time.
Entropy: A score from 1-250 that gives users insights into how hard their body is working.
AI assistant: Goyal has also mentioned that the wearable will feature a voice enabled AI assistant that can utilize motion sensors to detect vibrations from vocal cords and turn speech into text.
Several doctors, including Hepatologist Dr. Cyriac Abby Philips, who is also known as ‘The Liver Doc’, have voiced concerns about the science behind the wearable on social media. Other medical professionals including Dr. Jason Philip, have also raised concerns.
Temple uses optical sensing to gather physiological data. Optical sensors use light to analyze changes in light reflection or absorption from the area to which the device is attached.
This principle isn’t completely new and is already used in many consumer wearables that utilize photoplethysmography (PPG) to measure parameters like heart rate. However, this only measures changes in blood volume close to the surface of the skin.
The brain is mainly supplied by the internal carotid and vertebral arteries, whereas areas outside the skull are supplied by the external carotid artery. Doctors are questioning how the sensor would be able to measure blood flow in the brain when it is close to the temple. This means it could easily detect signals coming from blood vessels close to the surface of the skin. Additionally, there could also be changes in skin blood flow due to temperature, exercise, etc, affecting the optical sensor.
Another major concern is that there isn’t much independent science behind the wearable. Goyal has spoken about how there is research supporting the wearable, but this is preliminary research. This doesn’t mean there is independent validation.
The BloodFlow and Entropy metrics need to be assessed to see if they are accurate and useful. Independent researchers would need to look at how consistent the wearable is at measuring the desired physiological parameters.
Two publicly available research preprints have examined Temple's BrainFlow readings against established methods of studying blood flow in the brain.
The first study, published on medRxiv on September 4, 2026, involved 23 healthy adults. Researchers compared BrainFlow readings with transcranial Doppler (TCD) ultrasound, which measures the speed of blood flowing through an artery in the brain. They found that both measurements showed similar patterns of change during exercise and changes in body position. However, this does not establish that Temple can measure the exact amount of blood flowing through the brain. The study was funded by Temple Private Limited.1
A second study, published on bioRxiv on September 24, 2026, analysed 60 sessions involving 44 healthy young men. It compared BrainFlow readings with a technique called near-infrared spectroscopy, which uses light to study changes in blood and oxygen levels in body tissues. The researchers reported stronger correlations with signals estimated to come from the brain than with those from the scalp. However, the study was designed, funded and conducted by Temple Private Limited, and Deepinder Goyal was listed as an author.2
Both studies are preprints and had not undergone peer review at the time of reporting. They offer preliminary findings but do not establish Temple's clinical accuracy or show that it can diagnose neurological conditions. Further independent research is needed.
Some people have questioned the expertise of the scientific advisory board. Many have pointed out the importance of having experts in neurology, neuroscience, vascular physiology and biomedical engineering on board, for a wearable making claims about blood flow in the brain. However, having a science advisory board doesn’t mean there is independent validation of the science behind the product.
Deepinder Goyal has described Temple as a fitness and wellness device, not a medical device. However, how a product is classified matters because medical devices must meet specific regulatory requirements.
In India, medical devices are regulated under the Drugs and Cosmetics Act, 1940, and the Medical Devices Rules, 2017. A product's classification depends partly on what the manufacturer says it is meant to do. Devices intended to detect, monitor or treat diseases may fall under medical-device regulations.
The company said its BrainFlow and Entropy scores are based on emerging science and that some features may require regulatory approval in the future.
Goyal has spoken about how the claims are not overexaggerated. He stated that over $30 million has been invested in developing the technology, with around $20 million coming from himself.
He has also claimed that this was done because he is passionate about creating advanced hardware and health tech in India and not for short term gain.
Goyal also spoke about how this is not a medical device but a fitness and AI device. He also stated that it cannot be used to diagnose or prevent diseases and should not be used as a substitute to consulting medical professionals.
Regarding the research, Goyal stated that early research and preprints are part of developing new technology. He has mentioned that more research is being done.
On November 8, Goyal clarified that BrainFlow is not Temple's main focus. He said the company's primary focus is Entropy, a score intended to reflect how hard the body is working to maintain itself. He also acknowledged that the company had not yet published research on Entropy.
This raises further questions about how Entropy is calculated, what exactly it measures and whether the score has any proven scientific meaning.
Goyal has also discussed the Gravity Ageing Hypothesis, which suggests that gravity and the effort needed to maintain blood flow to the brain may influence ageing. However, this is still a hypothesis, not an established scientific explanation. The brain has a natural mechanism called cerebral autoregulation, which helps keep blood flow relatively stable when a person changes posture or experiences normal blood pressure fluctuations.
References:
1. Kumar A, et al. Concordance Between a Temple-Worn Optical Wearable and Transcranial Doppler During Exercise and Postural Transitions in Healthy Adults. medRxiv, September 4, 2026. https://www.medrxiv.org/content/10.64898/2026.09.02.26362022v1
2. Gulati D, et al. Evaluating Brain Flow Index from a temple-worn wearable against depth-resolved time-domain NIRS during head-down tilt and postural transitions in healthy young men. bioRxiv, September 24, 2026. https://www.biorxiv.org/content/10.64898/2026.09.17.751664v1
Rh/MF/MSM
