Apple Watch heart rate monitor teaser 001

A support document Apple published earlier this month contains a number of interesting tidbits and nice-to-knows regarding the Watch’s built-in heart rate monitor. We thought it’d be useful to give you a quick summation of the technologies the wrist-worn device uses to provide accurate readings of your heart rate.

The document also confirms that the Watch can connect wirelessly to external heart rate monitors such as Bluetooth chest straps for even more precise readouts.

All in all, Apple’s done a fine job outlining in Layman’s terms the tech and the sensors that measure a user’s heart rate, a feature many reviewers have described as seamless. In Apple’s parlance, it just works and here’s exactly how it works.

For starters, the Watch’s built-in sensor measures your heart rate and displays it right on your wrist, using the Heart Rate Glance. As a bonus, it keeps track of your heart rate every ten minutes, throughout the day, and stores the data in the Health app.

But how does it work?

The heart rate monitor is based on a difficult to pronounce technology called photoplethysmography. Wikipedia has more on that, but it basically comes down to using green LED lights paired with light‑sensitive photodiodes to illuminate your skin and measures changes in light absorption.

This lets the device detect the amount of blood flowing through your wrist at any given moment. Because blood is red, it reflects red light and absorbs green light.

“When your heart beats, the blood flow in your wrist — and the green light absorption — is greater. Between beats, it’s less,” reads the document.

Apple Watch heart rate monitor 001

Apple said it’s designed the sensor to compensate for low signal levels by increasing both LED brightness and sampling rate. That’s why the heart rate sensor on the back of the device flashes its LED lights hundreds of times per second, helping the device calculate heart rates precisely.

But when it measures your heart rate every ten minutes, the Watch switches to using infrared light. And if it fails to provide an adequate reading while using the infrared light, the device switches back to the green LEDs.

In order for the sensor to work as advertised, the Watch must be close to your skin. The company advises tightening the band in case the sensors aren’t reading your heart rate accurately.

All in all, the heart rate sensor in the Apple Watch is a great feature, especially if you’re something of a fitness buff. It checks your heart rate during workouts for an at-a-glance overview of both the intensity level and the heart rate change over time.

Apple Watch Health and Fitness Activity for iPhone web screenshot 001

This is crucial, as having continuous readouts of one’s heart beat in the Health app is indispensable when correlating your workouts and heart rates. In addition to your heart rate reading, the Watch collects other data to provide estimate on calories burned.

Aside from the heart rate sensor itself, it may tap into other sensors depending on your activity. In one example, running indoors prompts the Watch to use its built-in accelerometer.

But go cycling outdoors and the Watch starts using the GPS in your iPhone, if available, to track your activity with great precision in order to provide as accurate estimate on calories burned as possible. We also know the Watch learns about your stride enough over time to start accurately track workouts without an iPhone.

“And even when you’re not in a dedicated workout, it tracks how much you move each day,” notes Apple.

How do you like the Watch’s heart rate monitor?

Is this something you’d deem useful, even if you don’t hit the gym?

Source: Apple

  • Maxim∑

    So this could be the first real smart watch heart rate monitor that’s actually accurate. Fitbit is crap and so is the 360’s/LG Gwatch R’s heart rate monitor

    • Merman123

      Yep. Joanna Stern from the Wall Street Journal has given it a big thumbs up. Comparing it even to devices meant specifically for heart rate monitoring.

    • Looks like it, although it certainly isn’t better than dedicated Bluetooth heart rate monitors that cost just as much, if not more.

      • J M

        “Just as much, if not more”, what bluetooth heart rate monitors are you looking at? Even the most highly rated ones rarely push past $75…

      • Seriously?

        Just go to Amazon and browse the Heart Rate Monitor category and list only those priced >$200

      • J M

        Those are watches, trainers, or sometimes even GPS watches with HR functionality included, they are (minus a few exceptions) not a “dedicated Bluetooth heart rate monitor”, which is what I and Tommy Gumbs are referring to.

      • Tommy Gumbs

        Yea I don’t what he is talking about. Bluetooth HR’s aren’t pricey. I have 4 Garmin HR moniters all under 50 bucks.

  • It all looks wonderful; but Hello; we are going to have to Lose our beloved jailbreaks when we install 8.3; unless there is a breakthru soon….

    • I sooo fell you there, am not looking fwd to giving up my jail break. I am still running 8.1 and with the last update for the emojis people are txting me and I can’t see them but that doesn’t bug me because am holding on lol But soon I wont be able to .

    • John

      Not the end of the world if you lose your jailbreak mate, just letting you know that.

      • deepdvd

        Except that it’s like being forced to use a completely different phone. It’s rather devastating when you’re used to it.

      • John

        Oh dear. When you start throwing around words like FORCED and DEVASTATING, you really have to wonder what sort of idiot you are.

        No offence, but there’s more important things in this world then if you can jailbreak a bloody phone.

        The one thing you have to remember is that no one has FORCED you to buy an Apple Watch or indeed update your phone so relax a little and if its meant to happen, it will happen.

      • deepdvd

        LOL… hence the word, “like”. Ever heard of empathy? Try it sometime.

  • @munchkinsdad

    My drs have a hard time monitoring my heart fibs. This my be the perfect thing…

  • tmdlkwd

    This here:

    “The document also confirms that the Watch can connect wirelessly to
    external heart rate monitors such as Bluetooth chest straps for even
    more precise readouts”

    A great option and alternative, if needed, to use or compare to Apple HRM accuracy

  • misterz

    If the heart rate monitor is fairly reliable and accurate, Apple Watch becomes much more interesting to me. I am waiting for reviews from real users and perhaps v2 before jumping in.

    • Joey_Z

      this technology has been developed for a while now, and I’m sure Apple can get it right.

  • Joey_Z

    I’ve been using Mio Alpha for running and swiming for about 2 years. it uses the same technology, at least the green leds look very similar. it’s fairly accurate, (usually +/- 2-3 beats compared to my chest strap). I use it for 40 minutes of cardio a day, 6 days a week, and it can go on for 2 months on a single charge. So those LEDs are not as battery hungry as one would think.

  • David Pomerleau

    Really would like to disable the heart rate monitor completely. I’m sure it would save a good bit of battery. Probably won’t be able to until someone jailbreaks the Watch though.

    • Rowan09

      LEDs are very battery friendly.

    • Joey_Z

      you can probably save 1 minute of battery life per day by turning if off.