Everyone sleeps. But not everyone sleeps well. And the quality of your sleep can have far-reaching effects on your mental and physical health.

Considering all that, it’s no surprise that sleep health has become one of the major focuses of consumer-facing digital health plays — although research has shown that it’s less popular than diet or exercise tracking, and most popular among the “worried well”.

The digital health options for tracking and improving sleep are already extensive, and they’re expanding all the time. Read below for an overview of the different kinds of consumer-facing sleep tracking technologies on the market, which demonstrate the range of approaches that are currently out there.

1. Wrist wearables

Most wrist-worn wearable companies at this point offer sleep tracking these days.

In fact, although the brand is most associated with activity tracking, Fitbit has actually tracked sleep since the very beginning, though the integration of heart rate tracking into many of its wearables has upped the ante somewhat.

Today, Fitbit supports sleep tracking on the Alta HR, Inspire, and Charge 2 among other devices, and features include sleep stage tracking, silent alarms, a sleep schedule app, and sleep insight reports.

The Withings Steel HR, the athlete focused WHOOP, Garmin’s vivosmart devices, and many other wearables on the market all have sleep tracking features.

Only the Apple Watch currently, and notably, omits sleep tracking from its manufacturer-supported feature suite. But that may change in the next two years.

And even now, Apple Watch users can set the sensors in the device to track their sleep by downloading a wide variety of third party apps. The trick is finding time to charge the device, which currently doesn’t last much longer than a day on a charge.

2. Rings

Not all wearable sleep trackers are worn on the wrist. In fact, a couple of leading entries take the form of rings. With more than $20 million in funding, Oura Ring is one of the more promising entrants in this category, and even caused a bit of a stir when it showed up on Prince Harry’s finger last fall.

The Oura ring hosts a number of different sensors designed to monitor the wearer’s health while they sleep or engage in physical activities. These include an NTC body temperature sensor, infrared LEDs to actively measure blood volume pulse and an accelerometer and gyroscope to detect movement. The wearable feeds all of these readings through an accompanying app that generates insights and behavior change suggestions for the user.

Other sleep trackers on the finger include Motiv and Thim, which boasts a sleep conditioning program designed to help train the body to fall asleep faster.

3. Other Wearables

Some wearables don’t fit neatly into one category or the other. Eversleep, for instance, resembles a bracelet and a ring put together, a form factor that allows it to measure blood oxygenation.

Beddr’s Sleep Tuner device is a small adhesive patch that’s worn on the forehead. The sensor measures blood oxygenation, heart rate, and sleep position, as well as stopped breathing events. It’s been validated at the UCSF Hypoxia Lab, which found that the device had a margin of error of plus or minus 2.2 percent compared to arterial blood draw. 

And then there’s Rythm’s Dreem, a sleep tracking headband which actually measures brain activity, something most sleep trackers don’t. The headband uses dry polymer electrodes to track a user’s brain activity during sleep, generating data for analysis on an internal CPU. It also actively works to help users fall asleep and have more restful slumber by emitting a series of subtle, precise sounds directly to the inner ear via a process called bone-conduction technology. 

4. Apps

Do you even need a device to track and improve your sleep? Some companies say no. Using sensors like the phone’s accelerometer and microphone, some apps purport to track sleep simply by instructing the user to place the phone by the bed.

For instance, SleepScore Labs, the consumer-facing spin-out of Resmed backed by Dr. Oz, released a standalone app last year that uses the phone’s speakers as a SONAR system by projecting inaudible soundwaves around the bedroom. Once these reflect off of the user’s sleeping body and are captured by the smartphone’s microphone, the app’s algorithms translate the readings into a one- to 100-point metric of sleep quality.

Other apps, like  Big Health’s Sleepio app and the heavily-venture-backed Calm app don’t provide sleep tracking, but do offer medititation and coaching tools to improve sleep. Sleepio can incorporate tracking data from a number of other devices

5. Bedside devices

Some of the heaviest-hitting devices focused exclusively on sleep are bedside devices, like Withings Aura or Sleepscore Labs’ SleepScore Max.

Withings’ device, which debuted in 2014, consists of both a sensor placed in the user’s bed and a bedside device that serves as both lamp and alarm clock, which are controlled by a companion iOS app. The bed sensor monitors body movements, breathing cycles and heart rate, while the bedside device senses ambient environmental factors like noise, light, and temperature. The bedside device also emits light and sound to help users fall asleep or wake up. While Withings still offers limited support for the Aura, it appears to have discontinued it in favor of Withings Sleep (see below).

SleepScore Max is a consumer product based on Resmed’s technology that also powers the clinically-focused S+ device. The device, which looks like a small speaker, measures a number of different sleep-affecting variables including respiration, body movement, duration, and environmental qualities such as temperature and light. With these, the device and its companion app assign’s the user’s nightly sleep a 1 to 100-point rating as well as suggestions on how best to improve the rating.   

6. Under-the-mattress sensors

Several consumer offerings take the form of under-the-mattress pads like Apple’s Beddit device, Fullpower’s Sleeptracker device, and Withings Sleep. (EarlySense’s sensor is an enterprise version of this form factor).

Originally a Finnish crowdfunding phenomenon, Beddit was snapped up by Apple in 2017. The strap uses ballistocardiography (BCG), a method which uses motion sensing to detect individual heartbeats from cardiac contraction forces and breathing rhythm from chest wall movements. The strap measures bed time, awakenings and bed exits, sleep time, sleep latency (the time it takes to fall asleep), testing heart rate, sleep quality and breathing movements, which also analyzes if the user is snoring. From there the strap uses Bluetooth to connect with the companion app, which offers personalized coaching, a wellness diary, a history of sleep recordings and a social sharing option.

Similarly, Sleeptracker’s system consists of two sensors placed under either side of a bed, which connect via wifi to a companion app. It automatically tracks sleep phases, time awake, breathing rate, heart rate and more, and an AI system turns this trend data into actionable suggestions.

Withings Sleep (formerly Nokia Sleep) is another strap-style sensor which monitors sleep cycles, heart rate and snoring, and then displaying scores and suggestions to users through the companion Health Mate App. A recent update added support for tracking breathing disturbances by montioring respiration rate, heart rate, motion and snoring and logging any events through the night.

7. Smart beds

Finally, bed and mattress company’s aren’t about to miss out on the opportunities of the sleep monitoring space. Sleep Number’s 360 Smart Bed senses a user’s movements and adjusts their bed to enhance sleep, as well as delivering a “Sleep IQ” score. Last year they teamed up with the NFL to give the beds to players in the league.

Eight, a startup with $27 million in funding, offers both a smart mattress and a standalone sensor that can be placed atop the mattress. Paired with a smartphone app, the mattresses monitor various sleep factors such as heart rate or respiratory rate to discern patterns in the users’ sleeping habits.