(Pocket-lint) - The Apple Watch Series 6 and Apple Watch SE smartwatches sit alongside the older Apple Watch Series 3. The Series 5, Series 4Series 2, Series 1 and the original Apple Watch are all discontinued through Apple. 

To make matters simple, we've compared the Apple Watch Series 6 to the Watch SE and Watch Series 3 here so you can see exactly what the differences and similarities are, whether you're looking to upgrade or take the smartwatch plunge.

For the avoidance of doubt, the Series 6 is very similar to the now-gone Series 5 with a few new features.

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Apple Watch Series 6 vs Watch SE vs Series 3: Design and display

  • Series 3: 11.4mm thick, 5ATM waterproof, OLED Retina display with Force Touch
  • Watch SE: 10.7mm thick, 5ATM waterproof, LTPO OLED Retina display with Force Touch
  • Series 6: 10.7mm thick, 5ATM waterproof, LTPO OLED Always-On Retina display with Force Touch
  • All straps compatible across all models

The Apple Watch Series 3 features a solid rectangular body with the Digital Crown and separate button on the right, along with a speaker and microphone on the left. It's swim-proof up to 50-metres and it features Ion-X glass on top of the display. The GPS and Cellular model is differentiated with a red accent on the Digital Crown.

The heart rate monitor is positioned on the underside of the watch body, along with the release buttons for switching out the straps and the second-generation OLED Retina display sits on top, two times brighter than the Series 1 at 1000nits. 

The Apple Watch Series 6 and Watch SE both stick with a familiar design and same strap mechanism as the Apple Watch models that have gone before them, but there are a couple of differentiating factors between them and the Series 3.

In the case of the Series 6 (and Series 4 and 5), the Digital Crown has an electrical heart rate sensor built into it, which is in addition to the optical heart rate sensor on the underside of the watch cases. The Watch Series 6 also has a blood oxygen sensor, which is the main differentiating factor between it and the Series 5 and 4.

Meanwhile, both the Series 6 and the Watch SE have a much larger display than the Series 3 with rounded edges, making full use of the space available and resulting in a bolder design. The 40mm Series 6 and Watch SE models offer a 759sqmm2 display area compared to the 563sqmm2 on the 38mm Series 3, while the 44mm Series 6 and Watch SE models have a 977sqmm2 display area compared to the 740sqmm2 of the 42mm Series 3.

The larger display ratio makes the Series 6 and Watch SE (as well as the Series 4 and 5) look quite different from the Series 3 despite a similar design overall. In addition to the display increase, the Apple Watch Series 6 also offers an Always-On Retina display, which the Watch SE doesn't.

The Always-On display means you don't have to raise your wrist to wake the display up, with the screen always visible. A raise of the wrist or a tap on the display will brighten the Series 6 (and Series 5) display instead.

Apple Watch Series 6 vs Watch SE vs Series 3: Models

  • Series 3: Aluminium only options, two colours
  • Watch SE: Aluminium only options, three colours, Nike model in two colours
  • Series 6: Aluminium (five colours), Stainless steel options (three colours), Titanium options (two colours), Nike+ models and Hermès models
  • GPS and GPS and Cellular options for Series 6 and Watch SE
  • Size options: 38mm/42mm (Series 3), 40mm/44mm (Series 6 and Watch SE)

When the original Apple Watch launched, its case was available in aluminium, stainless steel and special materials like solid gold, all of which came in two size options of 38mm and 42mm.

The Series 3 then introduced a ceramic model, but this was discontinued when the Series 4 arrived. It was relaunched on the Series 5 but it has been discontinued again following the launch of the Series 6. There is are two titanium options though.

The Series 3 is now only available with an aluminium case, either silver or space grey. It comes in comes in 38mm and 42mm size options, but it is only available in a GPS only model, with no GPS and Cellular option available. There is also no Nike model.

The Watch SE also only comes in aluminium but there are three colour options, comprised of silver, gold and space grey. Size options are 40mm and 44mm and there are GPS only and GPS and Cellular models available. The Watch SE also comes in Nike models, available in silver and space grey.

The Series 6 has a lot more finish options available than the Watch SE and the Series 3. Like the Watch SE, it comes in 40mm and 44mm sizes, as well as GPS only and GPS and Cellular models. There are five aluminium colours - silver, space grey, gold, blue and PRODUCT(RED). There are then three stainless steel models - silver, graphite (DLC) and gold (PVD). Lastly, there are two titanium models - natural titanium and space black.

Additionally, the Series 6 also comes in Nike models - all of which are aluminium and come with Nike straps - and Hermès models - all of which are stainless steel and come with special Hermès straps. The Hermès models are all GPS and Cellular as standard.

While all the standard Series 6 models and the Nike models come in both case sizes though, some of the Hermès models only come in either 40mm or 44mm, not both.

Apple Watch Series 6 vs Watch SE vs Series 3: Hardware

  • Series 3: S3 processor, W2 wireless chip, Bluetooth 4.2, altimeter
  • Watch SE: S5 processor, W2 wireless chip, Bluetooth 5.0, fall detection, compass, always-on altimeter
  • Series 6: S6 processor, W3 wireless chip, Bluetooth 5.0, U1 chip, electrical heart sensor, blood oxygen sensor, fall detection, compass, always-on altimeter
  • Series 3/SE/6: Ambient light sensor, built-in GPS, optical heart sensor, accelerometer, gyroscope, 802.11b/g/n 2.4GHz Wi-Fi, 18-hour battery life 

The Apple Watch Series 3 has a dual-core processor called the S3 under its hood, coupled with a wireless chip called the W2. The GPS only model has 8GB of memory.

The Watch SE has a dual-core processor called the S5 - said to be 2x faster than the S3 - though it is coupled with the same wireless chip as the Series 3 - the W2.

The Apple Watch Series 6 has an upgraded processor claimed to be 20 per cent faster than the S5, called the S6. It also have the next generation wireless chip called the W3.

Both the GPS only and GPS and Cellular models of both the Watch SE and Series 6 have 32GB of memory, though of course the GPS and Cellular model has LTE connectivity. The LTE connectivity means you can make and receive calls and text messages, as well as perform all the tasks you'd want to on your Watch without your iPhone in range. It also works for Family Setup.

All the Watch models being compared here have built-in GPS, optical heart rate sensor, speaker, microphone, water resistance up to 50 metres, emergency SOS, gyroscope and an ambient light sensor. They also all offer Apple Pay.

The Watch SE and Series 6 add an always-on altimeter - the Series 3 has a standard altimeter - a built in compass, second generation optical heart rate sensor, international emergency calling and fall detection thanks to the improved accelerometer that offers up to 32 g-forces instead of up to 16 g-forces as found in the Series 3. It's worth noting that all of these features - except the always-on altimeter - can be found on the Series 4 and 5 too.

On top of those additions, the Series 6 also adds a blood oxygen sensor and an electrical heart rate sensor for ECG. The Series 4 and 5 have the ECG feature but not the blood oxygen sensor.

Apple Watch Series 6 vs Watch SE vs Series 3: Software

  • All run WatchOS 7 
  • Extra features on Series 6

The Series 3, Series 4, Series 5, Series 6 and Watch SE all run WatchOS 7.

All generations from the Series 3 and later therefore all offer a similar experience, even if there are a few extra features on the Watch Series 4, Series 5 and Series 6 like fall detection and the ECG function (US/UK/Europe only for now), as well as the Always-On Display, built-in compass and blood oxygen monitoring on the Series 6. Remember the Series 5 also has the Always-On Display and compass, while the Watch SE has the compass and fall detection.

You can read all about WatchOS 7 in our separate feature.

Apple Watch Series 6 vs Watch SE vs Series 3: Price

  • Series 3: From $199/£199
  • Watch SE: From $299/£269
  • Series 6: From $399/£379

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The Apple Watch Series 3 is the cheapest way to get your hands on Apple's smartwatch through Apple itself, with a starting price of $199/£199 for the GPS only model. There is no longer a GPS and Cellular model so the Series 3 isn't compatible with Family Setup.

The Watch SE starts at $299/£269, which is $100/£110 cheaper than the starting price for the Series 6. 

The Apple Watch Series 6 with GPS only starts at $399/£379 for both the standard model and the Nike model. The Apple Watch Series 6 with GPS and Cellular starts at $499/£479 for the standard model or Nike model, but this increases to $699/£649 if you want a stainless steel model.

The Apple Watch Edition models (titanium options) start at $799/£799. The Hermès models start at $1249/£1199.

Apple Watch Series 6 vs Watch SE vs Series 3: Conclusion

If you didn't invest in the original and you've decided the Apple Watch is now something you want, buying the Series 3 over the Watch SE or Series 6 will save you money, but you miss out on some key features and your finish options are much more limited.

Opting for the Watch SE over the Series 6 still saves you money - albeit not as much as the Series 3 - and you still get the bigger display design and many of the latest features, including a built-in compass, always-on altimeter, fall detection and the second generation optical heart rate sensor. 

The Apple Watch Series 6 of course offers the most advanced hardware of the three models being compared here, as well as the most finish options, but your wallet will take a hit too. Compared to the Series 3, if you have the cash it delivers plenty of worthy upgrades, not least the design that makes far better use of the display space.

Compared to the Watch SE though, the Series 6 only adds an always-on display, ECG, blood oxygen monitoring, a faster processor and the U1 chip. All the other features remain the same. For some, the improved processor, ECG and blood oxygen functionality, Always-On display and U1 chip could be the five features you needed to take the smartwatch plunge, but for others, the Watch SE will more than suffice.

In terms of upgrades, those with the original Apple Watch, Series 1 or Series 2 will see some worthwhile differences by switching to the Watch SE or Series 6, especially with the new display. Those with the Series 3 will also see a decent difference in the new models.

If you already have the Series 4 or Series 5 and you're wondering whether to upgrade to the Series 6, you may not need to this time around unless you really want blood oxygen monitoring, real time elevation data, or the always-on display if you are a Series 4 user.

Writing by Britta O'Boyle.