Deepinder Goyal, founder of Zomato and Eternal, has revealed six colours for Temple, his experimental wearable designed to monitor signals associated with brain blood flow and a metric called Entropy.
The update comes as the device moves closer to its commercial launch, with Goyal saying pre-orders could open as early as next week. People who have already joined the early-access waitlist will get priority when bookings begin.
The launch edition colours are True Gold, Rose Gold, Black Mirror, Real Jade, Deep Blue and Purple Funk. Until now, the device had largely been seen in a gold finish.
In a post on X, Goyal said, “Six colors for the launch edition of temple. Pre-orders open soon, hopefully next week; just need certainty on a couple more items. Folks on early access waitlist get priority access.”
A wearable designed for the temple
Unlike conventional smartwatches and fitness bands, Temple is worn on the side of the head, close to the temple between the forehead and ear.
Goyal, 43, has described the latest version as the smallest wearable on the market by volume. In an earlier update, he said Temple had become less than half the size of the version previously shown and described it as the smallest wearable on the market by volume.
He has also said that living and training with Temple could significantly change how users understand their bodies and performance. The limited launch edition is expected to ship before the end of 2026.
The device is being developed around BrainFlow, a technology intended to continuously track changes associated with blood flow to the brain. Goyal has also recently identified scientists involved in developing the BrainFlow technology.
BrainFlow and the Entropy metric
One of Temple's central functions is measuring changes related to blood flow to the brain. According to Goyal, BrainFlow is designed to continuously monitor these changes through the small device positioned near the temple.
A recent validation update shared by Goyal said Temple's BrainFlow showed a stronger relationship with changes in brain blood volume than changes in scalp blood volume. The findings are still being evaluated, however.
Temple also displays a metric called Entropy. Goyal describes it as a measure of the body's real-time “cost of being alive”, reflecting what he says is the body's metabolic and sympathetic demand.
The figure changes with factors including sleep, stress, exercise, caffeine and meditation. Goyal has said it is updated every second and presented on an index ranging from 1 to 250, with the lowest readings associated with deep rest and the highest levels recorded in elite athletes at peak output and flow.
He has described Entropy as something affected by virtually everything a person does, from sleeping and experiencing stress to sprinting, drinking coffee and meditating.
The device has also been described as capable of tracking measures associated with cognitive load, stress and fatigue. The underlying idea is that continuously collected information could help users understand how their bodies and brains respond to physical and mental demands.
However, these readings should not automatically be interpreted as signs of neurological disease or brain injury. Wearable measurements are different from a clinical diagnosis, and concerning symptoms still require assessment by a healthcare professional.
How Temple collects its signals
Temple is positioned on the side of the head and uses light-based sensing technology to collect signals from tissues and blood vessels. Such sensors can detect changes associated with blood flow and oxygenation.
The sensing process is challenging because light must pass through several layers, including the skin, scalp, blood vessels, muscle and skull, before information associated with deeper tissues can be assessed.
Dr Arun L Naik, an AIIMS-trained neurosurgeon, has questioned whether measurements taken at the temple can accurately represent blood flow in deeper brain arteries. He has stressed that Temple should not be treated as a substitute for established neurological investigations.
Other neurologists have similarly raised questions about whether measurements taken at a single external location can reliably represent blood flow throughout the brain. Established investigations such as angiography, CT angiography, MRI angiography, Doppler ultrasound and transcranial Doppler are already used for clinical assessment of cerebral blood flow.
What doctors say about its medical use
The medical debate around Temple centres on the distinction between a consumer wearable and a clinically validated diagnostic device.
Dr Naik has said that although the device represents an interesting piece of consumer technology, it cannot replace clinical investigation. Experts have raised particular concerns about whether signals from superficial vessels near the temple can accurately reflect activity or blood flow in deeper parts of the brain.
A separate neurologist cited by The Indian Express also questioned whether measurements from one location could reliably explain changes across both sides of the brain or across deeper and smaller arteries. The report noted that proper validation would require experimental testing, human studies and long-term research to establish whether the measurements have meaningful clinical value.
For now, Temple is therefore being positioned as an experimental health wearable rather than a replacement for medical tests or neurological evaluation.
With six launch colours now announced and pre-orders potentially opening next week, the device is moving closer to its limited commercial launch, although its exact pre-order date and several final details have yet to be confirmed.