Like the thirsty cast members of The Bachelorette, Samsung Aura and, if
rumors are correct, [music] Apple all want to put a ring on it. And why not?
The promise of a smart ring is undeniably sexy. A screen-free titanium
hoop that tracks your vitals 24/7. Who wouldn't want it? But, like a reality TV
marriage, buying a smart ring is sometimes followed by regret. If you've
ever wondered why your smart ring thinks you were napping while you were working
and yet misses your PR at the gym, that's because, turns out, shrinking an
entire lab's worth of equipment down to the size of a piece of jewelry requires
some serious engineering compromises. Compromises that could be fat-fingering
your biometric data. Let's break these devices down, starting with the main
sensor. [music] PPG, or photoplethysmography, is a fancy name
for shining light into your skin and measuring how much bounces back. In a
hospital, they'll clip a sensor onto your fingertip, yield transmissive PPG.
It's incredibly accurate because the signal is unobstructed. Smartwatches, on
the other hand, use reflective PPG, where the sensor and the photodiode are
on the same side. Fun fact, by the way, they use green light because your blood
absorbs it like a sponge, providing a high-contrast signal. Depending on, you
know, how far apart your photodiode is, if it's, say, on the curvature of a
ring, you may actually kind of be between these modalities, where you're
somewhat like in a transflective approach. You may see behavior of both
like a reflective and a transmissive PPG. Smart rings can occupy a weird
middle ground. Because the sensors wrap around your finger, light travels
further through your skin than it would from a smart watch. This gives the ring
a slight signal advantage, but it's one
that unfortunately gets dragged down by the constraints that arise from its size
>> [music] >> and from its battery. >> The amount of light you need in order to
measure an appreciable pulse is proportional also to the active area of
the photodiode that you're using to sense it with. So, a bigger photodiode,
a bigger sensor, means you can use less light, less current, in order to perform
the same relative measurement. If you only just shrink the photodiode itself,
you're going to be decreasing your your signal-to-noise ratio
and have to, you know, boost your LED light in order to accommodate for that.
You can think of it kind of like listening to a conversation in a crowded
bar. A smartwatch stands next to a person with a large, directional
microphone. A smart ring, on the other hand, is trying to hear them from across
the room using a tiny little spy mic taped to their collar,
which brings us to the battery. The Samsung Galaxy Watch Ultra packs 590
mA hours. >> [music] >> The Galaxy Ring,
17 to 22 and 1/2. And yet, the ring
claims it lasts for up to 7 days. How? Well,
because it doesn't. Both devices use duty cycling to extend their usable
charge time, but because the watch has a larger battery, one intense session
isn't going to drain it. The ring, on the other hand, has about
the battery of a Cheerio. [music]
They have also large dormant periods, where the ring simply is not measuring
at all. And and so you can kind of think of it as like interlacing on top of
interlacing, you know, in order to [music] make it so maybe you only measure the pulsations, measure the
heart rate, pulse ox, you know, for a minute, you know, every 10, 15, 20
minutes, for example, in order to to keep conserving uh power. [music] To put
this in perspective, when the Franklin Research Lab built their own DIY smart
ring, the battery gave out after about 4 to 6 hours of continuous use. So, if we
take that as a baseline for true continuous tracking, to survive a full
168-hour week of nonstop data collection, you'd need to wear 34 rings
and swap them out like ammunition magazines. By Wednesday, you'd look more
like the Divination instructor at Hogwarts than like a fitness enthusiast.
>> [music] >> The reason that smart ring bands can claim a week while Dr. Franklin gets
only 5 hours >> [music] >> is the sampling rate. When a researcher
says continuous, they usually mean high-frequency sampling. When a consumer
wearable says continuous, they often mean, "Ah, we check in every now and
then, and then we interpolate a bit so the graph looks like a solid line." And
if you have a darker skin tone, the LEDs actually have to work harder to get a
readable signal, which can cut that already slim battery life nearly in
half. [music] Now, that isn't to say that the form factor has no benefits. There is a
reason that hospitals clip sensors onto your fingers. They are densely packed
with arteries that are right close to the surface of the skin. But for smart
rings, that's kind of a double-edged sword. Besides being so darn cute and,
[music] you know, fingery, fingers are your body's temperature control meat
sticks. When you have vasoconstriction or dilation
uh due to being cold or due to, say, being in a sauna, that will, again,
change the distribution of blood within the skin and impact your
photoplethysmography signal. Typically, vasoconstriction
or having that blood redistributed away from the surface of
the skin can have a detrimental effect on the PPG. So, it'll decrease your
pulses, it will decrease your signal-to-noise ratio, and then the
opposite is true when you have perfusion. Cold hands equals a weaker
signal, which equals your ring struggling to find your pulse. Lock
outside in the winter or sit next to an aggressive air conditioner, and your
ring huh might think you're a spooky vampire with no pulse. Or Sam Altman.
Unlike the finger, the wrist sits closer to the body's core, [music] staying
warmer and maintaining more consistent blood flow, giving the watch a natural
edge in colder environments. But hey, I mean, if sitting still in a freezing
room isn't your only hobby, what about if you actually exercise?
Even a simple jog is going to slosh your blood around enough to give the sensors
a headache. But for hand heavy lifting, the ring becomes basically decorative.
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credit card required. When someone tightly grips a steering
wheel or a barbell, we typically call this motion artifacts. At the uppermost
level of your skin, you have a capillary bed, and when you apply pressure to this, that's the first layer that
actually gets compressed. And so you end up with a a large spike in your photoplethysmography signal. That's not
attributed to your pulsations or your heart rate, which is the thing we want to measure. These motion artifacts and
pressure-induced [music] signal loss hit simultaneously, and they compound fast.
White-knuckling a barbell squeezes blood out of the very capillaries the ring is
trying to read. So, by the time your heart rate has climbed to 160 beats per
minute mid-set, the ring might be reporting a breezy 80. A quick
TechQuickie safety tip, by the way, wearing a metal ring during heavy lifts
is not a good idea. Beyond scratching the finish of your ring, you're actually
risking a degloving accident. Seriously though, do not Google that. The standard
way to deal with motion artifacts is to cross-reference the accelerometer data.
If motion exceeds a specific threshold, then the PPG data just gets discarded
entirely because a gap is better than a wrong number. A 2024 study even found
that you might need to discard up to 70%
of heart rate variability readings due to poor signal quality. To combat this
data trashing, researchers are working on transformer-based AI models to
reconstruct corrupted PPG signals. So, the sensor's tiny, the battery prevents
continuous tracking, cold hands kill the signal, gripping blinds it, and most of
these rings aren't even FDA-regulated medical devices, making them pretty much
high-end accessories with an asterisk. So, are they an overpriced piece of
e-waste? Actually, no. There is one time of day
where almost all of these problems disappear, >> [music] >> and that's during sleep. Unless you're
David Goggins, you're probably aren't gripping a barbell in your sleep, so
your hands are relaxed and your arteries are right at the surface. Smart rings
can get incredibly accurate resting data
while being far more comfortable to sleep in than this darn thing. Aura even
boasts about their .999 correlation with medical-grade ECGs for
resting heart rate, which checks out. Even with a few misbeats, basic average
is easy. Their .984 HRV correlation claim, however, has a massive catch.
Heart rate variability measures millisecond differences between individual beats, and it needs [music]
beat-to-beat continuity. So, a gap in the data doesn't just reduce accuracy,
it invalidates the entire measurement window, which is why smart rings filter
out low-confidence data before reporting. To legally be able to claim
this HRV accuracy, many validation studies use sedentary participants. In
one, no subject's heart rate broke 90 beats [music] per minute, so it's kind
of easy to be accurate when your user's just vibing on the couch. As for the
high-level scores, like sleep score, readiness, and stress, those are
proprietary algorithms that arguably don't mean much. It's kind of a way of
gamifying your sleep to see who [music] can have the most readiness, I suppose,
and to help you justify your $5.99 monthly subscription for the rest of your life. If you want to see the
testing facilities that smart wearables, like rings, are designed in, check out
this video where I visited one in China. It's actually, for all of the dunking on these devices
that we just did, a lot more elaborate and way cooler than you might think.