Garmin Index Sleep Monitor Review

Introduction

The Garmin Index Sleep Monitor is Garmin’s first foray into the world of screenless wearables. This isn’t quite a Whoop rival if that’s what you were hoping for, though. 

While worn on your arm, the Index’s primary job is to monitor your sleep. It can’t track other data beyond that, but if you wear a bulky Fenix 8 during the day and don’t like the idea of taking it to bed, this is really what the Index is about.

In what could be a precursor to Garmin making a Whoop and Oura rival in the future, we’ve been wearing the Index to find out if it’s worth strapping on.

Design and fit

• Two strap sizes, machine washable
• Removable sensor
• Waterproof up to 50 metres

The Index is composed of a small module that features the type of optical sensor technology also found in Garmin’s watches and many other smartwatches. The sensor fits inside a soft band made from a blend of nylon and spandex, which also provides some stretch. Garmin uses Velcro to keep it securely in place on the upper arm and reduce the need for any more rigid material that could make it uncomfortable to wear at night.

Garmin usefully does offer advice on the best way to wear it when setting things up inside the Garmin Connect app. You’ll want that sensor facing your skin and ideally positioned on the outside of your upper arm. It doesn’t matter which way the sensor is sitting; the key is to ensure it establishes close and constant contact with the skin. For side sleepers, the idea is to wear it on the arm you’re not going to roll and lie on.

On my first attempt to test the Index, I clearly didn’t get that positioning correct. I’m not sure whether it was due to placement, ensuring the band was secure enough, or making sure the sensor was positioned close enough to my arm. The next morning, when I tried to sync my data, there was nothing to see in the Garmin Connect app. 

Perhaps Garmin needed to offer a clearer indicator of when the Index is successfully tracking which is also obvious to see when the band is on. 

There is a small indicator on the sensor that can emit vibrations, primarily to support the available intelligent wake alarm mode. You can also wake up the sensor by placing your finger on the sensor for five seconds, but you’re sort of going in blind, hoping the sensor is in prime position most of the time.

The band is a bit bigger than I anticipated it would be, and it could certainly benefit from having a better ratio between sensor and strap size. I can also appreciate that having more material around that sensor should reduce the chances of the sensor moving around. 

Comfort-wise, it’s generally been fine. I am a side sleeper and often change which side I sleep on during the night, which resulted in lying on top of the sensor at times. It wasn’t uncomfortable to do so, but that sensor is noticeable when you roll onto it.

It’s nice to see that the band is machine washable (once you remove the sensor first), as I imagine it will start to get a bit grubby after a few months of wearing it. That’s thankfully not been the case after a few weeks of testing. 

While you don’t want to drop the sensor in the wash, it is waterproof up to 50 metres in depth, offering the kind of protection against moisture found in many smartwatches and sports watches.

Garmin offers the strap in either small to medium or large to extra-large sizes, so there should be something to fit most arms. I was happy with the overall fit of the smaller-sized strap. Using velcro to secure the strap makes sense from a comfort point of view, but I’d be interested to see how well that velcro holds up over longer-term use. If you do need to replace the strap, you’ll need to pay £35 to do that. That’s not exactly cheap.

Tracking and performance

• Tracks sleep, heart rate, temperature and stress
• Works with Android and iOS
• Up to 7 nights of battery life

Essentially, the Index sees Garmin take the sleep tracking technology from its watches and put it inside a different form factor. One that some might prefer taking to bed rather than a watch or anything else on their wrist.

It utilises an accelerometer motion sensor, similar to most smartwatches, to detect when you’ve fallen asleep and when you’ve woken up in the morning or during the night. It also features Garmin’s latest Gen 5 Elevate optical sensor technology, delivering heart rate tracking, Pulse Ox readings, stress monitoring, breathing rate tracking, and skin temperature monitoring during the night. 

There isn’t the ECG support you will find on some Garmin watches, which also include the latest Elevate setup.

This data can also be used to power Garmin’s Body Battery energy monitor to help you assess the energy reserves you have for your day. It will also fuel many of Garmin’s other useful insights, including Training Readiness and recovery time suggestions. It also uses the onboard skin temperature data to power insights for Garmin’s women’s health features.

There’s an additional sleep-related feature in the form of a smart wake-up alarm that emits a gentle series of vibrations to the arm to wake you up in a gentler fashion. It’s not a new feature to smartwatches in general, but for Garmin watches, it was only recently introduced on the Vivoactive 6 before being rolled out to other Garmin watches.

When the tracking is done and you remember to whip the band off, it should automatically sync with the Garmin Connect app on your Android phone or iPhone as long as the two are close together.

From an accuracy point of view, I’ve found Garmin’s sleep tracking to be generally a little hit and miss. Thankfully, things have improved significantly in recent years, and I’d say the Index actually performed quite well, with most nights largely in line with the Oura Ring 4, Ultrahuman Ring Air, and a host of other reliable sleep-tracking smartwatches I wore alongside it.

For data such as sleep duration, times fallen asleep and woken up, as well as metrics like heart rate and heart rate variability, it reported similar data to reliable sleep trackers like the Oura Ring 4. Digging into sleep stages, there are a few more discrepancies to see in the breakdown of deep, light and REM sleep stage cycles. If you’re primarily focused on insights like sleep duration and having a tracker that can detect when you fall asleep and wake up, the Index seems to do that job fine. 

As far as going beyond what a Garmin watch will track and tell you about your sleep, that’s where I expected a bit more from the Index. It feels like Garmin missed an opportunity here to provide a sleep stat or insight akin to its Training Readiness one, which would make it a bit more appealing to non-Garmin users. 

Battery life for the Index is slated as up to seven nights’ worth of tracking. I’ve found that battery drop overnight has been on average around 10%, which suggests closer to 9-10 days of battery. I should add that I’m not regularly hitting the magic 8-hour sleep duration on most nights, so I imagine a more disciplined sleeper should see something closer to that over the week.

If you’re already a Garmin watch owner, you’ll be happy to see that it uses the same charging cable that comes with most watches now. When it reaches its lowest level, it can take as long as two hours to fully charge. The indicator light on the sensor will flash red when the battery is low, and you can also view battery status in the device section of the Garmin Connect app.

Should you buy it?

FAQs