Actigraphy and Wearables: Tracking Sleep at Home

Most people think they know how much they sleep. You go to bed at 11 p.m., wake up at 7 a.m. - that’s eight hours, right? But what if you were awake for two of those hours, just lying still, staring at the ceiling? Your brain says you slept. Your body says otherwise. That’s where actigraphy comes in - a simple, non-invasive way to track your real sleep, not the sleep you think you had.

Actigraphy uses a small device, usually worn on the wrist like a watch or ring, that measures movement. It doesn’t record brain waves or breathing like a sleep lab. Instead, it watches how much you move. No motion? Probably asleep. Lots of motion? You’re awake. Sounds basic, but it’s surprisingly accurate over time. The technology started in the 1980s with bulky research tools, but today, it’s inside your Fitbit, Oura Ring, and even some smartwatches. These devices have become the most practical way to monitor sleep outside of a hospital - and they’re changing how we understand rest.

How Actigraphy Works - Beyond the Motion Sensor

Modern actigraphy devices use three-axis accelerometers. That means they detect movement in every direction: up and down, side to side, forward and back. Every tiny shift - rolling over, tossing an arm, even shifting your fingers - gets recorded. The device samples this data 100 times per second (100Hz), capturing details a human could never notice.

But here’s the catch: the device doesn’t decide if you’re asleep. It just records motion. The real magic happens in the software. Algorithms take that raw movement data and apply rules based on decades of sleep research. For example, if you haven’t moved for 10 minutes straight, it assumes you’re asleep. If you move for more than a minute, it marks you as awake. These rules aren’t perfect. They can’t tell the difference between deep sleep and quiet wakefulness. But they’re good enough to spot patterns over days and weeks.

That’s why actigraphy shines in long-term tracking. A sleep study in a lab might show you how you sleep one night. But actigraphy can show you how you sleep over 30 days. That’s when you start seeing real trends - like how your sleep changes after work trips, during stress, or after drinking coffee after 3 p.m.

What You Can Actually Measure

Actigraphy doesn’t give you a full sleep profile like a sleep lab. It won’t tell you if you’re getting enough REM or deep sleep. But it gives you four key numbers that matter more than you think:

• Total Sleep Time: How many hours you actually slept, not how long you were in bed.
• Sleep Onset Latency: How long it takes you to fall asleep after turning off the lights. If this is over 30 minutes most nights, something’s off.
• Sleep Efficiency: The percentage of time in bed that you actually spent sleeping. A score below 85% for several nights in a row is a red flag.
• Wake After Sleep Onset (WASO): How many minutes you’re awake after falling asleep. Frequent nighttime awakenings? This number will tell you.

These metrics don’t lie. If your sleep efficiency drops from 92% to 74% over two weeks, you’re not imagining it. Your body is telling you something. And that’s the power of actigraphy - it removes guesswork.

Medical Grade vs. Consumer Wearables

Not all devices are created equal. There’s a big difference between a $1,800 medical-grade actigraph and a $99 fitness tracker.

Devices like the Philips Actiwatch Spectrum Plus are FDA-cleared for clinical use. They collect raw, unfiltered data. Doctors use specialized software to analyze it, looking for patterns tied to insomnia, circadian disorders, or shift work sleep problems. These devices are trusted in sleep clinics.

Consumer wearables - like the Oura Ring, Fitbit Charge 5, or Garmin Venu - use similar motion sensors, but their algorithms are tuned for general wellness. They estimate sleep stages (light, deep, REM) using heart rate and body temperature, which adds guesswork. A 2022 Stanford study found these devices were only 70-75% accurate at distinguishing REM from light sleep. That’s fine if you’re just trying to get more rest. But if you’re trying to diagnose a disorder, it’s not enough.

Still, consumer devices have improved. Newer models now integrate light exposure and skin temperature to improve wake detection. Garmin’s 2024 update, for example, improved wake detection accuracy by 16% by combining motion with heart rate variability. That’s a big step forward.

What Actigraphy Can’t Do - And Why It Still Matters

Let’s be clear: actigraphy won’t diagnose sleep apnea. It can’t detect pauses in breathing. It won’t catch restless leg syndrome or narcolepsy. For those, you still need a polysomnography (PSG) test - the full lab sleep study.

But here’s where it changes lives: paradoxical insomnia. This is when someone believes they sleep only two hours a night, but their actigraphy shows they slept six. Their brain is awake, but their body is resting. Without actigraphy, doctors might think they’re exaggerating. With it, they can finally see the truth. That’s why sleep specialists now use actigraphy as a first step - not to diagnose, but to validate.

Another use case? Circadian rhythm disorders. If you’re always tired at 3 p.m. or wide awake at 2 a.m., your internal clock might be off. Actigraphy tracks your activity over weeks. It shows when you’re most active, when you rest, and whether your rhythm lines up with daylight. This helps doctors adjust light exposure, melatonin timing, or even work schedules.

How to Use It Right - And Avoid the Pitfalls

Wearing a tracker doesn’t fix your sleep. How you use it does.

• Wear it on your non-dominant wrist. If you’re right-handed, wear it on your left. Misplacement can throw off data by up to 22%.
• Don’t take it off for naps or long breaks. If you remove it for more than two hours a day, the data becomes unreliable. Consistency is key.
• Track for at least 7 days. One night means nothing. You need a full week to see your real pattern.
• Ignore single-night spikes. Sleep varies naturally. A 30-minute difference from night to night is normal. Look at trends over time.
• Don’t obsess over scores. If you start stressing because your “sleep efficiency” dropped to 82%, you’re creating orthosomnia - sleep anxiety caused by tracking. Focus on how you feel, not the number.

And don’t rely on sleep stage estimates. Those are educated guesses. Your total sleep time and wake-ups are the real gold.

Who Benefits Most?

Actigraphy isn’t for everyone. But it’s life-changing for some:

• People with chronic insomnia who feel like they’re not sleeping - even when they are.
• Shift workers trying to adjust their sleep to odd hours.
• Travelers with jet lag - 82% of frequent flyers in one study improved their sleep schedule after using actigraphy for four weeks.
• People with circadian rhythm disorders like delayed sleep phase syndrome.
• Those trying to track treatment progress - like after starting CBT for insomnia or adjusting melatonin.

If you’ve tried sleep hygiene, meditation, or supplements and nothing changed, actigraphy might be the missing piece. It doesn’t cure anything. But it shows you what’s really happening - so you can fix it.

The Future - And the Warning

The tech is getting smarter. Researchers at the University of Michigan are training AI to detect wakefulness by combining motion, skin temperature, and even sound. The NIH just funded a $2.8 million project to improve wake detection by 27%. Apple is rumored to be adding a dedicated sleep study mode to the Apple Watch later this year.

But there’s a dark side. Most consumer apps send your sleep data to the cloud - often without end-to-end encryption. Your sleep patterns could end up in marketing databases, insurance risk profiles, or employer wellness programs. A 2024 Senate hearing raised alarms about insurers using sleep data to adjust premiums. That’s not science fiction - it’s already happening.

And then there’s orthosomnia. The fear of not sleeping well enough because your ring says you’re not. That’s a real problem. Tracking should empower, not terrify.

Actigraphy isn’t magic. It’s a mirror. It shows you what you’re doing - not what you should be doing. Use it to learn. Don’t use it to punish yourself. The goal isn’t a perfect score. It’s better rest.