Best External Heart Rate Monitors for iPhone and Apple Watch iMore 2019

The Apple Watch has an excellent oximeter-based heart rate monitor for tracking your day and basic workouts, but it's not perfect for more endurance or weight-based activities. For those tough workouts, you should consider an external heart rate monitor like Scosche's Rhythm+ Monitor Armband.

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 a workout, 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 a lot of exercises involving wrist bending or quick movement. The oximeter works by measuring the movement of your blood using light, and 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 grey 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 at all, you can use external monitors with your iPhone to get valuable heart rate data.

We've tested several Bluetooth heart rate monitors, and the best of the best.

Best for Most: Scosche Rhythm+ monitor armband

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 primary tests with it in that location, as well.) It uses an 8-hour rechargeable battery, so you can plug it in after workouts like you might with an Apple Watch.

Both the small grey 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. From those workouts, it proved significantly more accurate 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 really designed to deal with major forearm or bicep flexion.

Unlike many of the 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.

Pros:

  • Lightweight
  • Breathable band
  • Frequent heart rate readings
  • Water resistant

Cons:

  • Tight fit when lifting weights

Best for Most

Scosche Rhythm+ monitor armband

An armband that monitors without fear of battery drain.

If you're looking to get better heart monitoring without going full in on the chest strap look, get this forearm-monitoring instead.

Best for Runners: Wahoo TICKR X heart rate monitor

The biggest difference between the TICKR X and the Polar H10 is in these little additional options, largely for runners: The TICKR lets you track your stride, ground contact time, and vertical oscillation. It's also less water-resistant, offering protection up to 5 feet versus the Polar's 30.

In my tests, I found the TICKR X slightly less reliable than the Polar H10, largely thanks to its RunFit app, which occasionally caused the TICKR to malfunction — there were several instances during a workout where it claimed my heart rate was up in the 170s (it was not). I also noticed occasional misfires on account of the vertical oscillation tracker — during Wahoo's 7 Minute Workout, it refused to log multiple exercises and reps on account of not seeing the movement.

That said, the TICKR X does have a friendlier look to both the workout app and overall experience; it markets itself as a Bluetooth chest strap for beginners, rather than Polar's fitness experts.

Pros:

  • Water-resistant
  • Stride tracking
  • Vertical oscillation tracking
  • Offline support

Cons:

  • Inconsistent readings

Best for Runners

Wahoo TICKR X heart rate monitor

If you're a runner, you'll love the data analysis.

This electrode-based neoprene chest strap offers up to 16 hours of offline tracking, water resistance, an app for tracking your workouts, and more.

Best for Apple Watch: 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 workout, get the ActionSleeve. It's the perfect alternative.

Pros:

  • Works with Apple Watch
  • More accurate readings thanks to positioning
  • Affordable

Cons:

  • Uncomfortable for bicep workouts

Best for Apple Watch

ActionSleeve

Lets you use your Apple Watch.

If you want to stick with the Apple Watch's heart rate monitor, but would like a little more accuracy, the ActionSleeve is the perfect wearable.

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 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 a number of 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.

Pros:

  • Accurate readings
  • Syncs with Health app
  • Onboard storage

Cons:

  • Chest strap style
  • Bad app design

Best for Accuracy

Polar H10 Heart Rate Monitor

Polar's technology provides speedy fitness tracking.

This water-resistant neoprene chest strap is slim and comfortable and offers electrode-based heart monitoring which is more accurate than other straps.

Best for Long Runs: 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 help you better understand where you need improvement.

Just like the Rhythm+, it uses both yellow and green optical sensors for better accuracy with all skin tones.

I tested the Rhythm24 with daily running sessions alongside my Apple Watch and found that the Rhythm24 was always more accurate, monitoring every heartbeat in real-time, as opposed to 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 to be 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.

Pros:

  • Water-resistant
  • Longest battery life
  • Multiple workout modes
  • Support for triathlon training

Cons:

  • Expensive

Best for Long Runs

Scosche Rhythm24

Great for fitness buffs that are in it for the long haul.

This heart rate monitor armband has 13 hours of continuous memory storage so you can leave your phone behind when you're long-distance training.

Bottom line

The Scosche Rhythm+ monitor armband 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.

If you're someone who's on the market for an external heart monitor that works and pairs perfectly with their Apple Watch, then the ActionSleeve is well worth taking a peek at. It's affordable, accurate, and ready to help you monitor your heart rate no matter what workout you decide to do.

Credits — The team that worked on this guide

Lory Gil is the current Managing Editor at iMore and has picked up the fitness mantel in Serenity's absence. 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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