A smartwatch leans on the phone in your pocket more than almost any other gadget. Apple's compatibility table pairs every Apple Watch with an iPhone, while Samsung and Google both say their current watches do not pair with iPhones, and some health features narrow the choice further still. This guide takes each decision in turn as the makers describe it: phone support, ECG and other health readings in the UK, battery life, GPS against cellular, payments and water ratings, then matches five watches to the phone you own.
Buy the watch that matches the phone. Apple says the Series 12 needs an iPhone 11 or later, Samsung says the Galaxy Watch9 works with Android phones but not iPhones, and Google lists Android 12 or newer for the Pixel Watch 5. Samsung's ECG and blood pressure app also needs a Galaxy phone. For a household with both kinds of phone, Amazfit lists Android and iOS for the Active 3 Premium.
Key Takeaways
- Apple lists an iPhone 11 or later for the Series 12 and SE 3, Samsung says the Galaxy Watch9 cannot pair with an iPhone, and Google says iPhones are not supported on Pixel Watch.
- Samsung says the Samsung Health Monitor app behind its ECG and blood pressure features needs a Samsung Galaxy phone, so a Galaxy Watch on another Android phone goes without them.
- Apple's feature availability page lists the UK for the ECG app, Irregular Rhythm Notifications and the Blood Oxygen app, which Apple says is for wellness only and not for medical use.
- Battery figures run from Apple's up to 18 hours for the SE 3 to Amazfit's up to 12 days of typical use for the Active 3 Premium, each under the maker's own tests.
- Apple and Google say a cellular watch must use the same network as the phone, with Apple listing EE, O2, Three and Vodafone, and Google EE, Three and Vodafone for Pixel Watch 5.
The Phone You Own Decides Which Smartwatch Works
Start with the phone, because the three big makers each draw a firm line. Apple's compatibility table pairs every current Apple Watch with an iPhone, and its spec pages say the Series 12 and SE 3 need an iPhone 11 or later, with iOS 27 or later for the Series 12. Apple lists no Android option.
Samsung's Galaxy Watch9 page says the watch works with compatible Samsung Galaxy phones and other supported Android phones, that the Galaxy Wearable app is needed for setup, and that pairing with iPhones is not supported. Many of its newer features, Samsung adds in the footnotes, need Android 13 or above. Google's Pixel Watch 5 spec page says it works with most phones on Android 12 or newer, with a Google Account and the Pixel Watch app, and Google's compatibility page states plainly that iPhones aren't supported.
Households with both kinds of phone have fewer choices. Amazfit lists Android 7.0 and iOS 14.0 for the Active 3 Premium on its product page, although the watch's own manual says iOS 15.0 or above.
Health Features Depend on the Phone and the Country
ECG apps, rhythm alerts and blood oxygen readings come with conditions. Apple's feature availability page lists the UK for the ECG app, Irregular Rhythm Notifications, the Blood Oxygen app and Hypertension Notifications. Its compare page offers the ECG app on the Series 12 but not the SE 3, and Apple's ECG support page says the app cannot detect a heart attack, blood clots or a stroke.
Samsung's Health Monitor page lists the UK for ECG, irregular heart rhythm notifications and blood pressure, but requires a Samsung Galaxy phone on Android 12 or higher. Blood pressure needs calibrating against a cuff every four weeks, says its Galaxy Watch9 page. Google lists the UK for its ECG app on Pixel Watch and for Loss of Pulse Detection on Pixel Watch 3 and later, but limits irregular rhythm notifications to select countries it does not name.
None of this replaces a doctor. Apple says the Blood Oxygen app is not for medical use, Google says only a doctor can diagnose AFib, and Amazfit's manual says the Active 3 Premium isn't a medical device.
Battery Life and Water Ratings Come With Small Print
Battery figures come from each maker's own tests. Apple gives the Series 12 up to 24 hours, or 38 in Low Power Mode, and the SE 3 up to 18, or 32. Samsung lists the 40mm Galaxy Watch9 at up to 40 hours with the always-on display off and 30 with it on. Google gives the 41mm Pixel Watch 5 up to 30 hours with the always-on display and the 45mm up to 40, so the bigger case lasts longer. Amazfit quotes up to 12 days of typical use for the Active 3 Premium, or 4 with the always-on display.
Apple rates the Series 12 to 50 metres under ISO 22810:2010 for pool and ocean swimming, but not scuba diving or high-velocity water sports. Google rates Pixel Watch at 5 ATM under the same standard and warns against soapy water and high temperatures. Samsung rules out diving on the Galaxy Watch9, and Amazfit says to remove the Active 3 Premium for a hot shower or sauna. Apple, Samsung and Google all say water resistance diminishes over time.
GPS Models Lean on the Phone and Cellular Models Need a Network
Apple, Samsung, Google and Amazfit all list built-in GPS on these watches. Calls and data are the difference. A GPS, Bluetooth or Wi-Fi model relies on the phone for those, while a cellular model connects by itself, and Apple and Google both say it shares the phone's number. Google's help page shows the watch's eSIM identifier, the EID, under SIM status in its mobile settings.
Apple says the iPhone and Apple Watch must use the same network provider, and that pre-paid and some older accounts aren't supported. Its cellular page lists Three, EE, O2 and Vodafone in the UK. Google's compatibility page sets the same rule for full talk, text and data, and lists EE, Three and Vodafone for Pixel Watch 5. Samsung's Galaxy Watch9 page says LTE availability depends on the country and carrier, but names no UK networks.
Safety features split the same way: Google says Loss of Pulse Detection on a Wi-Fi Pixel Watch needs the phone in Bluetooth range to call for help. All five watches in the table are non-cellular versions.
Contactless Payments Depend on the Wallet and the Bank
Paying by watch only works with a card the wallet accepts, so check the bank before relying on it. Apple's feature availability page lists the UK for Apple Pay, and Apple's spec pages say the cards come from participating issuers. On Pixel Watch, Google Wallet holds the card, and Google's help page says that once a card is on the watch, the phone isn't needed to pay, though a screen lock has to be set first.
Samsung offers two routes. Its UK Samsung Wallet eligibility page lists Galaxy Watch models from the Watch6 onwards, although its Galaxy Watch9 entries name only the LTE versions, and every phone on that page is a Samsung Galaxy model. The cards Samsung lists include Barclays debit cards, HSBC UK, Lloyds Bank, Monzo, Nationwide and Starling Bank.
Google's Wear OS help page adds the second route: tap to pay through Google Wallet needs a watch on Wear OS 2.0 or later with NFC, in countries where Google offers it. Samsung's spec list gives the Galaxy Watch9 Wear OS Powered by Samsung and NFC.
A Fitness Tracker Lasts Longer but Does Less
A smartwatch earns its frequent charging with apps, calls and payments. Anyone who mostly wants steps, sleep and heart rate may be better off with a band, and the fitness tracker comparison covers those in detail.
Google's own spec pages show the trade. The Fitbit Charge 6 lasts up to 7 days, works with iOS 16.4 or Android 11 and newer, and still has built-in GPS and sensors for the ECG app. The 41mm Pixel Watch 5 gets up to 30 hours with the always-on display and works with Android only.
Some watches sit in between. Amazfit's Active 3 Premium has a full watch screen, Bluetooth calls and five satellite positioning systems, with up to 12 days of typical use and up to 24 hours of continuous GPS. Amazfit's product page does not mention ECG or an LTE version, though.
Music is the other reason to choose a watch. Apple's battery test for the Series 12 includes a workout with music over Bluetooth, and the wireless earbuds guide matches buds to the same three phone makers.
Five Smartwatches Matched to iPhone, Galaxy, Pixel and Any Phone
Two caveats first. A watch bought for one phone loses features on another: a Galaxy Watch9 on a Pixel goes without Samsung's ECG and blood pressure app, and an Apple Watch does not work with Android at all. Chargers differ too. Apple includes a magnetic fast charger to USB-C cable but no power adapter, Google packs a Quick Charge Dock, and Amazfit's package list names a charging head with no cable, so the USB-C phone charger guide helps with the plug.
A 3-in-1 stand charges a watch, phone and earbuds together, as the wireless charger guide explains.
The table follows the phone. The Apple Watch Series 12 suits iPhone owners who want the ECG app, the Blood Oxygen app and Hypertension Notifications. The SE 3 is the cheaper iPhone choice, with irregular rhythm and sleep apnoea notifications but no ECG app. The Galaxy Watch9 is for Galaxy phone owners, and Samsung lists security updates until 31 July 2031. The Pixel Watch 5 suits Pixel and other Android 12 phones, with three years of security updates. The Amazfit Active 3 Premium is the budget pick for either phone.
| Product | Best for | Key specs | Price | |
|---|---|---|---|---|
 | Apple Watch Series 12 (GPS, 42mm) iPhone pick | iPhone owners who want the ECG and Blood Oxygen apps | Up to 24 hrs, 38 hrs Low Power Mode, ECG, 50 m water | Check price → |
 | Apple Watch SE 3 (GPS, 40mm) iPhone budget | iPhone owners on a budget who can skip the ECG app | Up to 18 hrs, 32 hrs Low Power Mode, 50 m, sleep apnoea | Check price → |
 | Samsung Galaxy Watch9 (Bluetooth, 40mm) Galaxy phones | Galaxy phone owners who want ECG and blood pressure | Up to 40 hrs AOD off, 30 hrs AOD on, 5 ATM, NFC | Check price → |
 | Google Pixel Watch 5 (Wi-Fi, 41mm) Pixel and Android | Pixel and other phones on Android 12 or newer | Up to 30 hrs with AOD, 48 hrs Battery Saver, 5 ATM, IP68 | Check price → |
 | Amazfit Active 3 Premium (GPS, 45mm) Budget | Long battery life on Android or iPhone | Up to 12 days typical, 24 hrs GPS, 5 ATM, Bluetooth calls | Check price → |