The Owlet sock is a wearable pulse oximeter designed for babies. It wraps around your infant’s foot and uses light-based sensors to continuously measure heart rate and blood oxygen levels while they sleep, sending that data wirelessly to a base station and your phone. The current version, the Dream Sock, is FDA-cleared as a Class II medical device for infants 1 to 18 months old, weighing between 6 and 30 pounds.
The Sensor Technology Inside the Sock
The Owlet sock works on the same principle as the pulse oximeter a nurse clips to your finger at the doctor’s office. It’s called photoplethysmography, which simply means shining light through skin and reading what comes back. Small LEDs on the bottom of the sock send light through the blood vessels in your baby’s foot. A detector on the other side measures how much light is absorbed. Because oxygenated blood and deoxygenated blood absorb light differently, the sensor can calculate oxygen saturation. The same light signal pulses with each heartbeat, which is how the sock picks up pulse rate at the same time.
To prevent false readings, the sock’s processing algorithm limits how fast reported values can change. Oxygen saturation can shift by no more than 1% per second, and heart rate by no more than 8 beats per minute per second. These caps match normal physiological limits, filtering out motion artifacts and signal noise that could otherwise trigger unnecessary alerts.
How Data Gets to Your Phone
The system has three parts: the fabric sock with its snap-in sensor, a base station that stays in your baby’s room, and an app on your phone. The sensor connects to the base station over Bluetooth. The base station then connects to your home Wi-Fi network, which links it to Owlet’s cloud servers and pushes data to the app. If Bluetooth pairing doesn’t work, you can set the sock up directly over Wi-Fi instead.
This two-step relay means the sock itself only needs a low-power Bluetooth radio, which helps with battery life. The base station handles the heavier lifting of maintaining a Wi-Fi connection and serving as the primary alert device in the room.
What the Notifications Mean
The base station uses colored lights and sounds to tell you what’s going on, and each color corresponds to a different level of urgency.
- Red (high priority): The base station flashes red and plays a loud tone when pulse rate drops below 50 bpm, rises above 220 bpm, or oxygen saturation falls below 80%. You also get a push notification on your phone.
- Yellow (medium priority): A flashing yellow light means the sock has a placement issue or has fallen off your baby’s foot and couldn’t get a good reading for at least 60 seconds. It also triggers if the sock moves out of Bluetooth range of the base station for that long.
- Lavender: A flashing lavender light means your baby has been moving excessively for an extended period. This is informational, not a health alert.
- Blue (low priority): A solid blue light with a soft tone means the sensor battery has about 50 minutes of charge left.
The app mirrors these notifications and also displays real-time pulse rate and oxygen saturation values. It tracks trends over time, so you can see how your baby’s readings relate to the preset alert thresholds across multiple nights.
What It’s Designed to Do (and Not Do)
The Dream Sock is cleared for monitoring healthy infants at home. It is not designed for babies who have already been diagnosed with a heart or lung condition. The FDA classification makes an important distinction: the sock is not intended to catch every single episode of abnormal heart rate or low oxygen. It only sends a notification when it has enough clean data to analyze, which means moments of heavy movement or poor sock placement may create gaps in monitoring.
The device is also not a replacement for traditional monitoring, diagnosis, or treatment. Its purpose, according to its FDA clearance, is to supplement your own judgment and prompt you to seek medical guidance if something looks off. Think of it as an extra set of eyes, not a medical-grade ICU monitor.
Getting an Accurate Reading
Because the sock relies on light passing through skin, fit matters a lot. The sensor needs to sit snugly against the top of your baby’s foot with the LEDs positioned correctly underneath. A sock that’s too loose, bunched up, or placed too far toward the toes will struggle to get a consistent signal, which is what triggers those yellow placement alerts.
Owlet sells different sock sizes to accommodate growth from 6 to 30 pounds. If your baby is outside that weight range, the readings become unreliable. Very small newborns under 1 month old fall outside the cleared age range entirely. On the upper end, once your child passes 18 months or 30 pounds, the sock is no longer sized or validated for them.
Skin irritation is a common concern with any wearable on a baby. Alternating which foot you put the sock on each night helps reduce pressure marks. Making sure the sock is clean and dry before each use, and that your baby’s foot is dry, also cuts down on skin issues.
Real-World Reliability
A study published in Global Pediatric Health analyzed data from 47,495 newborns using an earlier version of the Owlet sock. The alert thresholds in that version were slightly different (heart rate below 60 bpm triggered a red alert, compared to below 50 bpm in the current Dream Sock), but the underlying technology is the same. The study confirmed that the processing algorithm’s rate-of-change limits effectively filtered out non-physiological signal spikes.
That said, no consumer wearable matches the precision of a hospital pulse oximeter with a hardwired probe on a still patient. Motion, sock fit, skin pigmentation, and ambient light can all affect accuracy. The sock works best on a sleeping or resting baby in a dimly lit room, which is exactly how most parents use it.