If you don't have an Apple Watch yet, you should get one. And probably this one. Yes, it may seem expensive and extraneous if your already have an iPhone and maybe an iPad and laptop or whatever, but here's the thing: It can save your life in a way none of that other stuff can.

If you already have an Apple Watch, should you upgrade That depends. If you own a Series 3, I wouldn't rush to trade it in unless you use it to make calls all the time or see the upcoming ECG feature as a must-have feature.

Large screen; Good call quality; ECG capability; Fall detection; WatchOS 5 brings numerous improvements; Stylish

Expensive; Battery life remains unchanged; No built-in sleep tracking

Editor's note (Sept. 24): This review has been updated to reflect more impressions and results of iFixIt's Series 4 teardown .

Big; beautiful display; Advanced health sensors; Faster processing power; Useful Raise to Speak Siri

ECG app not available at launch; Expensive

The fourth iteration of the Apple Watch still looks like a tiny iPhone on your wrist, but for many, it was the most exciting device announced at Apple's event earlier this month.

Bigger; better screen; All old Watch bands fit on the Series 4; Good battery life; Faster performance; Fall detection has the potential to be lifesaving; ECG features give users more control to monitor their health on a daily basis; Accurate auto workout detection and ending feature; WebKit support...

ECG app isn't available yet; WatchOS 5 drops support for Series 0 devices; New complications are only compatible with new watch faces; Still no support for third-party watch faces; Still no native sleep tracking; Siri has trouble completing Shortcuts; More expensive than any other Apple Watch; and...

Apple takes unjustified heat for iterating on a product year after year. By not tossing out the whole platform and design, however, the company has created a game-changer with the Apple Watch Series 4.

Earlier Apple Watches were impressive wearables, but the new Series 4 is the strongest argument yet for wearing a smartwatch. And that's not just because of bigger, edge-to-edge screen or its improved fitness tracking either.

Roughly two-and-half minutes into my run, the watch kicks in. There's a haptic buzz on my wrist. "It looks like you're working out," the watch face reads. That's followed by a big, yellow button, suggesting I start an indoor run.

This is by far the best Apple Watch yet. If you have been contemplating buying one, now is the time. The screen has adequate realistate. Has a very good display and chocked full of useful features. The ECG feature works pretty good. The health apps are nice. Overall a very nice watch.

The Apple Watch has been updated for the fourth time in as many years, bringing with it a number of new features , and for those looking to upgrade from the first-generation model , there's a tweaked design which features a bigger screen and other cool new tech .

Bigger and more immersive screen looks superb; Same strap size despite new design; Will last you through a day

Electrocardiogram feature not available at launch; Some WatchOS 5 nitpicks; No battery improvement

We've covered only the most significant differences in the above comparison - we didn't even have time, for example, to mention the cool new dynamic watch faces available for the Series 4's larger screen. But hopefully you get the idea.