Best External Heart Rate Monitors iMore 2021
While the heart rate monitor on the Apple Watch is good enough for basic workouts, it may not be enough for marathon training or more intense workouts. That's because the Apple Watch only has so much battery life, and intense workouts can drain the battery faster than you'd think due to the constant heart rate monitoring. That's why we think you should get Scosche's Rhythm+ Monitor Armband for those hardcore workouts and intense training sessions because it's the best external heart rate monitor for Apple Watch.
- Best for Most: Scosche Rhythm+ Heart Rate Monitor Armband
- Best for Apple Watch: Twelve South ActionSleeve for Apple Watch
- Best for Accuracy: Polar H10 Heart Rate Monitor Chest Strap
- Best for Runners: Scosche Rhythm24 - Waterproof Armband Heart Rate Monitor
- Best for Training: Garmin HRM-Tri Heart Rate Monitor
- Best for Cyclists: Wahoo TICKR FIT Optical Heart Rate Monitor Armband
Best for Most: Scosche Rhythm+ Monitor Armband
We have tested the Scosche Rhythm+ Monitor Armband and can safely consider it the best external heart rate monitor for Apple Watch. The water-resistant (IP67) device connects to an adjustable neoprene strap. While you can wear it anywhere on your arm, Scosche recommends the forearm. (I did my initial tests with it in that location, as well.) It uses an 8-hour rechargeable battery, so you can plug it in after workouts as you might with an Apple Watch.
Both the small gray tracker and strap are slim and stylish, given that you'll likely be wearing them in a visible location on your arm. You can slip a shirt on over the Rhythm+ if you want to hide it, but it's a nice enough looking tracker to leave it visible. It does look a little goofy when both the Apple Watch and tracker are on the same arm, but until we have magical nanobot implants, such is our connected device lifestyle.
In practice, it's significantly more comfortable than wearing a chest strap during heavy-duty workouts while being about as accurate. The Rhythm+ uses green and yellow oximeter sensors (described as "PerformTek biometric sensor technology") to get a more precise look at your heart rate than the Apple Watch's green sensors alone and records data much more frequently.
I wore the Rhythm+ for a week to my regular skating practices and weight training sessions. It proved significantly more accurate from those workouts than my usual Apple Watch tracking (I used Bluetooth to connect to the Rhythm, but it also offers ANT+ support for cyclists). My only concern with the Rhythm+ was occasional tightness when doing arm-related exercises. Although the neoprene strap flexes slightly, it's not designed to deal with major forearm or bicep flexion.
Unlike many other chest strap options, Scosche doesn't offer a dedicated app for viewing your recorded heart rate data. Instead, you can look at it in Apple's Activity or Health apps or download a third-party option like Cardiogram.
Keep in mind that Scosche has announced the second iteration of this product, the Rhythm+2.0 at CES 2021. It will become available sometime in Spring 2021. But if you need the best external heart rate monitor for Apple Watch right now, then we still highly recommend picking up the original Rhythm+.
- Breathable band
- Frequent heart-rate readings
- Tight fit when lifting weights
Best for Apple Watch: Twelve South ActionSleeve
It's a band that you pop the case of your Apple Watch into and strap it to your upper arm. This keeps the Watch's sensor securely to your skin, so you get a more consistent reading, especially if you're bending your wrist a lot while you exercise.
Your Apple Watch, sans band, fits into a mount with the backside exposed, so the Watch's sensors are unobstructed. The mount has a raised silicone border to protect the Watch from scratches (and keep it in place).
If you're happy with the performance of your Apple Watch's heart rate sensor but don't want it wrapped around your wrist while you work out, get the ActionSleeve. It's the perfect alternative to the best external heart rate monitor for Apple Watch.
- Works with Apple Watch
- More accurate readings thanks to positioning
- Uncomfortable for bicep workouts
Best for Accuracy: Polar H10 Heart Rate Monitor
The H10 connects to your iPhone or Apple Watch using Bluetooth LE, though you'll want to use one of Polar's apps to get Polar's specific readings — I used Polar Beat. It's not my favorite app (and requires an in-app purchase if you want to see your heart rate/fat burn breakdown), but it does the trick. Your heart tracking will also log in to Apple's Health app after you connect it, allowing you to take your fitness data elsewhere. And if you're not near a connected device, the H10 has a small amount of onboard storage, allowing you to log a workout even without your devices present.
Note: We've seen several users run into an issue where the H10 appears on the iPhone, but not the Apple Watch. To fix this, you'll want to pair the H10 to the Apple Watch first before connecting it to your iPhone — or disable Bluetooth on your iPhone from the Settings app before attempting to pair with Apple Watch.
Polar's H10 was by far the most accurate of the fitness trackers I tried, but it does come at the expense of having to wear a chest strap. During a run or weight training session, this shouldn't bother you, but full-contact sports might be a bit much: For me, anything strapped to my chest in derby is a potential bruising hazard — and I've seen enough cracked sternums to want to avoid that fate at all costs. So if you can get past the fact that this has to be worn around your chest, then it can be considered another one of the best external heart rate monitors for Apple Watch.
- Accurate readings
- Syncs with Health app
- Onboard storage
- Chest strap style
- Bad app design
Best for Runners: Scosche Rhythm24
The Rhythm24 has a battery status indicator, so you'll know if it's time to recharge.
It has seven different monitor modes for different training options. Set it for running, cycling, swimming, just tracking your heart rate or heart rate variability for identifying stress and recovery during training. If you're training for a duathlon or triathlon, set one of the multi-modes, and it will track each of your different activities.
You can record your workout and save your training data to better understand where you need improvement.
Like the Rhythm+, which is still the best external heart rate monitor for Apple Watch, it uses both yellow and green optical sensors to better accuracy with all skin tones.
I tested the Rhythm24 with daily running sessions alongside my Apple Watch. I found that the Rhythm24 was always more accurate, monitoring every heartbeat in real-time instead of updating with new information that was already behind by the time it synced.
The Rhythm24 uses the same type of armband used with the Rhythm+. I found it very comfortable during my runs but have not tried it with weight training exercises.
For just a bit more than the Rhythm+, the battery life and multiple training modes make this a much better fit with fitness fans that workout for more than just an hour or two. If you're a long-distance runner, a triathlon trainer, or just want to track your heart rate all day long, get the Rhythm24.
- Longest battery life
- Multiple workout modes
- Support for triathlon training
Best for Training: Garmin HRM-Tri Heart Rate Monitor
When you're training hard, you want an external heart rate monitor that won't get in the way. The Garmin HRM-Tri is one of the smallest and lightest heart rate monitor offerings from Garmin, and it will remain comfortable throughout your training.
With the HRM-Tri, it's designed to best handle running, cycling, swimming, and many more intensive activities. The monitor uses a single CR2032 battery that can last up to 10 months if you just do an hour of training a day. The HRM-Tri even provides feedback on your running form and running dynamics thanks to the accelerometer that measures torso movement when running.
As you use the HRM-Tri, it can store up to 20 hours of heart rate data from your swims and training, and this data can be forwarded to other Garmin sports watches after your session. Or you can just send your data directly to the Garmin Connect app to view your swim metrics, heart rate graphs, pace, stroke, and more.
- Small and lightweight
- Comfortable to wear
- Long battery life
- Gives feedback on running form and dynamics
- Great for swimming
- Requires CR2032 battery
- Not rechargeable
Best for Cyclists: Wahoo TICKR FIT Heart Rate Monitor Armband
If you want to have the heart rate monitor that champions like Team INEOS, Bora-Hansgrohe, Katusha Alpecin, Ironman World Champion Jan Frodeno, Heather Jackson, and American Pro Mountain Biker Sonya Looney, then check out the Wahoo TICKR FIT.
The TICKR FIT is an armband that works best on your forearm, and you can get personalized heart rate training for more efficient workouts. With TICKR FIT, you'll track and capture your heart rate in real-time, see your training zones and calories burned on your iPhone through over 50 compatible apps since it utilizes Bluetooth/ANT+. This means it will work with not only your iPhone but tablets, GPS watches, and bike computers by Wahoo, Polar, Garmin, Apple, and many more.
If you use the Wahoo Fitness app with the TICKR FIT, you can automatically upload that data into your preferred training platform of choice, like Strava. And while it seems geared more for cycling, the TICKR FIT works well with any form of exercise. The TICKR FIT is quite accurate, comfortable, and stays in place as you exercise.
- Comfortable on the forearm
- Accurate readings
- Works with over 50 apps and many devices
- Up to 30 hours of battery life
- Affordable price tag
- No data stored on the device itself
Why bother with an external heart rate monitor?
Heart rate monitoring on Apple Watch comes at the expense of battery life: The smartwatch's health sensors account for a large majority of battery drain. As such, Apple limits how often the sensor records data, even during workouts. At rest, you'll get heart rate data every 10 minutes. During workouts, you're likely to get recordings every 10 seconds to a minute.
The wrist-based monitor can also get tripped up if you tend to do many exercises involving wrist bending or quick movement. The oximeter works by measuring the movement of your blood using light. When you flex your wrist, you can momentarily change that circulation, leading to erroneous heart readings (If you've ever seen an Apple Watch reading of "65bpm" or lower or a gray number when you're in the middle of a high-intensity workout, that's likely what has happened).
If you're worried about your Apple Watch's battery life during a lengthy workout (like a marathon, for instance), or you'd like more consistent and quick readings, consider an external heart rate monitor. These Bluetooth accessories often run off quick charges or watch batteries and offer faster readings from a location with better circulation (like the chest or upper arm). If you don't have an Apple Watch, you can use external monitors with your iPhone to get valuable heart rate data.
We've tested several of these Bluetooth heart rate monitors to give you the best recommendation, and the Scosche Rhythm+ Monitor Armband is the best external heart rate monitor for Apple Watch.
Get fit with the best external heart rate monitor for Apple Watch
The Scosche Rhythm+ monitor armband is the best external heart rate monitor for Apple Watch because it is a reliable, accurate, and affordable monitor that's perfect for amateurs and fitness fanatics alike. Not only that, but it's also an eye-catching accessory that's bound to turn heads while you work up a sweat.
Plus, it's significantly more comfortable than wearing a chest strap during heavy-duty workouts while being about as accurate. The Rhythm+ uses green and yellow oximeter sensors (described as "PerformTek biometric sensor technology") to get a more precise look at your heart rate than the Apple Watch's green sensors alone and records data much more frequently. And another great thing about Rhythm+ is the fact that since Scosche doesn't have its own dedicated app, your data just syncs directly with Apple Health; no other app is required.
Scosche is releasing an updated version of the Rhythm+2.0 soon. However, we will update this guide once it's available and put it through its paces.
Credits — The team that worked on this guide
Christine Romero-Chan is a Staff Writer at iMore trying her best to get back into a more active lifestyle. She has been testing out new devices and tools that will help get her back on track.
Lory Gil is the former Managing Editor at iMore who picked up the fitness mantle in place of Serenity, but she now works for Apple. She's been testing heart rate monitors on her daily morning jogs to make sure they meet our highest standards.
Serenity Caldwell was formerly the Managing Editor at iMore, and now works for Apple. She spent a year testing these heart rate monitors while working out, training for roller derby, and testing her body's limits.
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