Actigraphy and Wearables: How to Track Sleep at Home Accurately

Most people think they know how well they sleep. You lie down at 11 p.m., wake up at 7 a.m., and assume you got eight solid hours. But what if you were awake for two of those hours-completely still, eyes closed, no movement-and your brain never registered it? That’s the hidden flaw in self-reported sleep. This is where actigraphy changes everything.

What Actigraphy Actually Measures

Actigraphy isn’t magic. It’s a small device, usually worn on the wrist like a watch or ring, that tracks movement using a tiny accelerometer. Every time you shift, roll over, or sit up, it records it. Then, software turns that motion data into an estimate of when you’re asleep and when you’re awake. It doesn’t measure brain waves, eye movements, or breathing like a sleep lab does. It just watches your body.

The science behind it is simple: when you’re asleep, you move less. When you’re awake, you move more. Modern devices like the Oura Ring or Philips Actiwatch use tri-axial sensors that catch movement in all directions, sampling data up to 100 times per second. That’s more than enough to spot the difference between tossing and turning and lying perfectly still.

But here’s the catch: lying still while awake is the biggest blind spot. If you’re lying in bed staring at the ceiling, your device sees zero movement-and assumes you’re asleep. That’s why actigraphy can overestimate sleep time by 30 to 60 minutes in some people, especially those with insomnia. It’s not wrong. It’s just incomplete.

How It Compares to a Sleep Lab

Polysomnography (PSG) is the gold standard. You spend a night in a lab with wires glued to your scalp, chest, and legs. Sensors track brain activity, eye movement, muscle tone, heart rate, and oxygen levels. It’s accurate-95% or better at telling sleep from wake. But it’s also expensive, invasive, and only gives you one night of data.

Actigraphy doesn’t replace PSG. It complements it. While a sleep lab tells you what happened one night, actigraphy shows you what happened over 14 days. That’s huge. Sleep isn’t a one-night event. It’s shaped by stress, travel, caffeine, work schedules, and light exposure. A single night in a lab can’t capture that.

For example, someone with circadian rhythm disorder might sleep fine on the lab night because they’re in a quiet, controlled environment. But at home, they’re sleeping at 4 a.m. because their body clock is out of sync. Actigraphy catches that. So does a parent who thinks they’re sleeping through the night but is actually waking up every 45 minutes to check on their baby. The device doesn’t lie.

Consumer Wearables vs. Medical-Grade Devices

Not all sleep trackers are created equal. You can buy a Fitbit Charge 5 for $99 or an Oura Ring for $299. Both use actigraphy. But here’s the difference:

Medical-grade actigraphs like the Philips Actiwatch Spectrum Plus are FDA-cleared. They’re used in sleep clinics, research studies, and hospitals. They record raw, unfiltered movement data at high resolution. They’re designed for clinical decisions.

Consumer wearables? They’re designed for marketing. They take the same basic movement data but add layers of guesswork. They estimate REM sleep, deep sleep, and sleep stages using heart rate and skin temperature. But here’s the truth: no consumer device can measure REM sleep accurately without EEG sensors. That’s why 35% of Fitbit Charge 5 users complain about inaccurate sleep stage tracking on Amazon.

The numbers don’t lie. A 2022 Stanford study found Oura Ring data matched lab PSG for total sleep time within 8%-good enough for trends. But for REM detection? It was off by 40%. Consumer devices are great for spotting patterns. They’re terrible for diagnosing sleep disorders.

What You Can Actually Learn From Your Data

If you’re wearing a wearable to track sleep, focus on these four metrics:

• Total Sleep Time: How many hours you actually slept. Not how long you were in bed.
• Sleep Efficiency: The percentage of time in bed that you actually slept. Below 85% for more than a week? That’s a red flag.
• Sleep Onset Latency: How long it takes you to fall asleep. Consistently over 30 minutes? You might have sleep onset insomnia.
• Wake After Sleep Onset (WASO): How many minutes you’re awake after falling asleep. Frequent 10- to 20-minute wake-ups? That’s fragmented sleep.

Don’t obsess over sleep stages. Don’t panic because one night you got 5% REM. Look at trends. If your sleep efficiency drops from 92% to 78% over three weeks, something’s changed. Maybe you started drinking coffee after 3 p.m. Maybe you’re working later. Maybe you’re stressed. The device won’t tell you why-but it will show you that something’s off.

How to Use It Right

Wearing a tracker doesn’t make you an expert. Here’s how to get real value:

1. Wear it on your non-dominant wrist. Studies show misplacement cuts accuracy by up to 22%.
2. Wear it for at least 7 days. One night means nothing. Two weeks gives you a real baseline.
3. Don’t remove it for more than 2 hours a day. ActivInsights found that breaks longer than that reduce data validity by 18%.
4. Track your habits too. Write down when you drank caffeine, exercised, or used your phone before bed. Correlate it with your sleep data.
5. Ignore single-night outliers. Your sleep varies. A 45-minute difference from night to night is normal.

And don’t fall for the “Readiness Score” trap. That’s not sleep science. It’s a marketing algorithm that combines sleep, heart rate, and activity into a number you can’t verify. Focus on the raw data: time asleep, time in bed, how often you woke up.

Who Should Use It-and Who Shouldn’t

Actigraphy is most helpful for:

• People with insomnia who think they’re not sleeping at all (but actually are)
• Shift workers trying to adjust their sleep schedule
• Travelers dealing with jet lag
• People with delayed sleep phase disorder (falling asleep at 3 a.m. and waking at noon)
• Anyone monitoring treatment progress (like CBT-I or melatonin therapy)

It’s not for:

• People with suspected sleep apnea (it can’t detect breathing pauses)
• Those with restless legs syndrome (movement is the symptom, not the signal)
• Anyone using it to self-diagnose
• People who get anxious over sleep numbers (yes, orthosomnia is real)

The Cleveland Clinic says it best: actigraphy is for treatment monitoring, not initial diagnosis. If you’re struggling with sleep, see a sleep specialist first. Then use a wearable to track progress.

Privacy, Cost, and the Future

Most consumer sleep apps send your raw movement data to the cloud-without end-to-end encryption. That’s a problem. Your sleep patterns are deeply personal health data. If a company gets hacked, or sells your data to insurers, it could affect your premiums or coverage. In 2024, the Senate held hearings on this exact issue.

Cost-wise, medical-grade devices run $1,200-$1,800. Most clinics rent them out for $50-$100 per week. Consumer devices? $99-$299. If you’re serious about tracking, start with a Fitbit or Oura. If your doctor recommends it for a sleep disorder, they’ll likely provide a medical-grade device.

The future? AI is improving wake detection. New algorithms are combining movement with skin temperature and light exposure to guess when you’re awake-even if you’re still. Apple’s rumored Sleep Study feature, expected in late 2024, could integrate heart rate variability and audio cues to better detect sleep stages. But the core truth won’t change: movement tells you when you’re asleep. It doesn’t tell you why.

Final Takeaway

Actigraphy won’t cure your insomnia. It won’t tell you if you have sleep apnea. But it will show you the truth about your sleep habits-without the guesswork. It’s the most reliable tool you can use at home to understand your sleep patterns over time.

Use it to spot trends, not to panic over numbers. Use it to talk to your doctor, not to replace them. And if you’re using it to chase perfect sleep scores? You might be making your sleep worse.