The new apple watch series 4 is a health and fitness game changer

So I welcome any help that makes me smarter, faster, better-at the office, at home with my family, and in my workouts. That’s why I’ve worn an Apple Watch almost every. single. day for the past 3.5 years. (True story: I put the first model on my wrist 48 hours after giving birth to my youngest son, George!)

Since Friday, I’ve been secretly testing the Series 4, which goes on sale today.

To cut to the chase: The new Apple Watch health and fitness features make it a powerful device for your overall well-being. That’s because game-changing bells and whistles have elevated the Apple Watch Series 4 from an investment-worthy health accessory to a sleek and beautiful device that actually might save your life.

The new heart rate sensor functionality is legit.

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Electrodes are embedded on the crown as well as the back of the watch, giving you the power to take your own electrocardiogram (EKG or ECG), which you can then send to your doctor as an encrypted PDF. It can also warn you if you have a potentially serious heart condition called atrial fibrillation (aka AFib or AF).

Roughly a year and a half in the making, this ECG functionality is approved by the American Heart Association as well as the Food and Drug Administration, which is a very big deal. (The ECG app will be rolled out soon but is not currently available.)

Apple was inspired to develop the ECG feature when it began receiving letters from customers who credited the Watch’s HRM feature for catching an abnormally high heart rate that signified a potentially deadly heart condition. The Series 4 also includes a low heart rate threshold to help catch bradycardia, a condition when blood is pumped too slowly in the body.

Those are the big health headlines, here’s more on my experience as a super-user....

The Series 4 display is 30 percent bigger.

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The speaker is louder, the design is sleeker. Everything runs zippier, and the crown now includes a cool haptic (vibrating) feature. The watch is also thinner, so despite the increase in screen size, the watch feels more subtle (in a good way) on my wrist.

Fortunately I haven’t needed the new fall sensor technology that comes with Series 4, but as a self-described bull in the china shop who trips through life, I’m happy it’s there. The Watch will ask if you need help immediately after sensing that you’ve fallen…no reply from you within one minute will trigger an SOS call to 911. Along with the ECG, I can imagine many millennials gifting the watch to their aging parents just for this feature.

As a runner, I’m also loving the new metrics you can track during jogs.

Cadence (how many strides you take per minute) is helping me hone in on my most efficient stride. Rolling mile pace allows me to see exactly how fast I ran the last mile of my run, no matter how far along I am. And the battery lasts up to six hours on outdoor runs, so you're good to go if you're training for a long race like a half-marathon or triathlon.

And maybe best of all, the new OS nudges you with a “did you start a workout?” prompt after a few minutes of activity. So you never have that Nooooo moment of realization that the Watch didn’t capture some of your mileage/HIITing/etc. It’ll also nudge you post-workout, so you don’t accidentally log a seven hour Pilates session.

The new OS also includes two new workout activities, yoga and hiking.

Having just returned to Brooklyn from a family trip in the mountains of Colorado, where I logged hikes as “outdoor walks” (carrying a 35-pound toddler on your back up 1,500 feet of elevation is not a walk!), I’m particularly excited to put this to use. And I don’t plan on waiting for my next vacation…part of my mom life is being a Sherpa...and carrying a backpack, two to three scooters, helmets and a bag of groceries up the hills of Park Slope, where I live, feels like a “hike” to me. Right?!

You can also challenge other S4ers to seven-day-long workout competitions, where users win points as they close their move, exercise, and stand activity rings. (I’m in the middle of one right now with Apple’s Julz Arney…and for the record, I’m winning! #smacktalk). I’m sort of always in friendly-competition mode with the girlfriends I share activity data with, so this challenge feature takes our healthy who-can-be-most-active feuds to a new level.

Apples unveiled awesome new watch faces that feel artistic and emotional.

You'll find liquid metal, vapor, water, and more-but I’m crushing on the face that features eight “complications” (data moments) in addition to the date and time. There are some Easter eggs, like a complication that shows the high, low and current temp and another that shows not only your activity rings, but exactly how far along you are in each one.

Back when George was a newborn and I wasn’t working out much, it was the cool productivity features like the texting from my wrist, Apple Pay and feeling blissfully untethered from my iPhone that won me over. But now that life has gotten even bigger, fuller and, yep, sweatier-from #ownyourmorning runs to marathon days at the office-I could not be more thrilled that the Watch has evolved into a powerful health and fitness accessory. I award it all of the gold medal emojis.

Available for purchase and order beginning September 21. The Apple Watch Series 4 starts at $399.