Video Overview


This year’s iteration of the Apple Watch can be your trainer, doctor, guardian, and now, live-in nurse! How’d Apple fit all these personalities into one watch? Let’s find out why everyone is falling so hard for this watch—with a teardown!

If you can’t get enough repair and teardown content, we have just the prescription for you: two to three Instagrams a day, Facebook during lunch, a newsletter once a week, and a tweet when the craving is too much.

This teardown is not a repair guide. To repair your Apple Watch Series 4, use our service manual.

  1. Apple Watch patient profile:
    • Apple Watch patient profile:

      • LTPO OLED Retina display with Force Touch

        • The Series 4 again comes in two sizes: 40 mm (324 × 394 pixels) and 44 mm (368 × 448 pixels).

      • Custom-designed Apple 64-bit dual-core S4 SiP (System in Package)

      • Optional LTE and UMTS, built in GPS/GLONASS/Galileo/QZSS, NFC, Wi-Fi 802.11b/g/n 2.4 GHz, and Bluetooth 5.0

      • Improved accelerometer and gyroscope, optical and electrical heart sensors, microphone, speaker, barometric altimeter, and ambient light sensor

      • Water resistance rating (up to 50 meters)

      • WatchOS 5

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  2. While these black squares may look outwardly similar, X-rays from our experts at Creative Electron reveal radically different insides.
    • While these black squares may look outwardly similar, X-rays from our experts at Creative Electron reveal radically different insides.

    • Already our subject (left) presents with some differences from the Series 3 (right)—the back sports an all-new optical sensor in the middle, surrounded by a new electrode.

      • We're looking forward to a closer look at that ECG hardware.

    • Other immediate differences from the "old" 42 mm version: the corners are noticeably rounder for more of that squircle look, and the side button now sits flush with the case.

    • Seen from the side, the Series 4 is noticeably slimmer than the Series 3 (by 0.7 mm)—but it's actually thicker than the original.

      • From the look of things, a good deal of that slimming is thanks to the new display.

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    • A quick checkup on the all-ceramic-and-sapphire-crystal back details:

      •  Watch, check.

      • Series 4, check.

      • A laundry list of features, including water resistance to 50 meters.

      • Optical sensor, right in the middle this time.

      • Big ring-shaped electrical sensor—that's new.

    • Inside one of the wrist band slots, we find a new model number, A2008—and in the other, the serial number, plus a small air vent hole for pressure equalization.

    Outstanding job on these (as well all the others) photos! Thank you

    Nikon1 - Reply

    I wonder how they print that serial # in there.

    ktappe - Reply

    Hello friend that serial is printed by a robot with a special bit, Apple can also customize those engravings in the idevices if users prefer it, thanks for commenting...

    Miguel -

    I think the marking and texts are laser engraved.

    Carver Tang - Reply

    • Swinging our iOpener pendulum back and forth, your crown is getting heavier and heavier. Your wristbands sink into the cushions... Hey Siri, turn on DND.

    • Now we can place our blade under the edge of this shiny display without scaring our patient.

    • This approved method has been tried and tested on several occasions, although we've yet to determine how much water resistance is restored afterward.

    • With its familiar trinity of cables safely unplugged, we can take a closer look at the display.

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    • With the screen in isolation, we get a better look at the contours of the new display. The extra pixels and increased screen-to-body ratio come thanks to rounded-off corners, a la iPhone X, XS, and XS Max.

      • The 44 mm model's display now covers 977 sq mm, compared to 740 sq mm on the 42 mm Series 3.

      • Meanwhile, the 40 mm model spans 759 sq mm, versus 563 sq mm on its 38 mm predecessor.

    • On the back we spot three chip packages, of which two are sealed shut, while the third bears no markings whatsoever behind its metal shield.

    • If past history is any guide, this is where the touch controller and NFC chips are hidden. We'll update if we can get a positive ID.

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    • On our way to the battery, we encounter the now-standard tri-point. Sorry pentalobe, Apple seems to have a new favorite these days.

    • Disconnecting what we think is the battery leads to a moment of confusion as we realize the battery is still tethered down by its flex cable. So what did we just disconnect?

      • Probably wasn't important... right?

    • The actual battery flex cable has been rerouted from its location on the Series 3, and now lies sandwiched underneath the battery and above the main board. With that dispatched, let's pop it out!

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  3. Spread Fixmas Cheer
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    • Here's the built-in battery powering the Watch—no self-winding action here!

      • This is a 1.113 Wh (291.8 mAh at 3.81 V) power pack, labeled A2059.

        • ... Or it might be 1.12 Wh, depending on which side of this battery you believe.

        • Regardless, that's down about 17% in capacity from the 1.34 Wh of the 42 mm Series 3 (although still more than the 38 mm model's 1.07 Wh battery from our most recent teardown).

    • Now who wants to do the math on volume? 0.7 mm thinner but 2 mm taller comes out to …

    • … just enough to give the battery its daily 18 hours of runtime, apparently!

    Hello.Small correction to the battery.

    1.07 Wh is in the watch 38mm series 3.

    The watch 42 mm is 1.34 Wh

    Series 4 44 mm has 1.113 Wh is less about 20%

    Dariusz - Reply

    Hi Dariusz, you’re right. It is indeed 20% less than the 42 mm Series 3. Our Series 3 Teardown was a 38 mm Version. I will edit the step to avoid confusion.

    Tobias Isakeit -

    So battery capacity is the same for both 40mm and 44mm?

    vman699 - Reply

    The 44mm lasts a little longer

    Miguel -

    Same question as vman699. Do the 40 and 44mm sizes both have the same capacity battery?

    louhobby - Reply

    Official numbers from Apple:

    40mm: 0.86 Wh

    44mm: 1.12 Wh

    38mm: 1.07 Wh

    42mm: 1.34 Wh

    nozukanatake - Reply

    What about battery capacity of GPS vs LTE?

    anonymous 9856 - Reply

    Can I have the exact dimension of the battery: LxWxT? Thank you!

    Mr Jiang - Reply

    • After the battery connector's hide-and-seek shenanigans, we're more prepared for a Force Touch gasket switcheroo.

    • Its flex connector now lies in the completely opposite corner, with twin cables that are stacked instead of spread out side-by-side. Very streamlined.

    • That Taptic engine, by contrast, looks about the same as we remember it, if a little squashed-looking. Let's have a closer look.

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    • Here we have the component responsible for shaking things up—the Taptic Engine, also known as an electromagnetic oscillating linear actuator.

    • Compared to the shakers of yore, this is a much thinner design, but it's also longer.

    • Even this smaller engine takes up a lot of room in this tiny device—room that could have gone to a bigger battery, but Apple seems to feel physical feedback is very important.

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    • Next up, we surgically remove the new noisemaker—that's alleged to be 50% louder, and maybe harder, better, faster?

    • Now that the microphone has migrated over near the digital crown, the speaker can take advantage of that space for more volume.

    • A silicone gasket seals the speaker to make its water-expelling magic possible, much like it did on last year's version.

      • The little black “eye” adjoining the speaker may be a barometric sensor, cleverly using the speaker grille’s access to the outside atmosphere. Since it no longer needs its own unsightly hole in the chassis as it did in Series 3, this is a victory for Jony Ives everywhere.

      • Update: It turns out there's a tiny tunnel from the air vent we saw in Step 3, passing through the chassis and right into the path of this little sensor. So it probably doesn't need any help from the speaker grille, but we still think it's most likely a barometer.

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    • Finally, we get to the core of all things: the Apple-designed S4 system-in-package.

    • Good news, everyone! The S4 is secured only with screws, and pops right out—a welcome change from the fiercely-glued SiPs of years past.

    • As always, the package itself is encased in a solid block of resin, meaning most of its secrets will be difficult to extract. Thankfully though, the RF components remain a little more exposed:

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    • In our effort to push out the heart sensor array, the whole bottom pops out. Turns out they weren't kidding about more access through the bottom case.

    • We spot a magnet in the middle for holding the Watch to the charger, the charging coil itself, and some new silicon:

      • A88 AY10

      • 18206 00D5

    • That's a very tidy array of black pads lying under the S4 package—possibly for heat dissipation? Or maybe they are just comfy pillows for keeping its stress levels low.

    Does it look like the foam is conductive?

    It also appears the bottom is just press-fitted with the O ring offering the water & dust sealing and wedge so the back doesn’t come off. For sure a better design than the glued backs in the older series. The trick will be getting the back on without damaging the O ring, a touch of scuba divers O ring grease will be needed.

    Dan - Reply

    Is the back a solid piece, or is the circular part in the center glued onto the back too as it was in the series 3?

    Mac 128 - Reply

    Any idea what kind of chips the A88 AY10 and 18206 00D5 are and who provides them?

    Alexandros Roussos - Reply

    • This golden donut is likely a streamlined antenna, as we've not seen the fiddly brackets or golden gaskets of yesteryear.

    • Meanwhile, we've come to the headline feature: new electrical heart sensors (ECG) to complement existing optical sensors.

      • The Apple Watch is a Lead I ECG, which means it's only measuring voltage between the right and left arms. The first electrode is on the Watch back, pressed against your wrist. The second is the crown, held by your opposite hand's fingers.

      • These electrodes detect tiny changes in electrical polarization across your skin as your heart beats. The S4 then interprets that data to compute and analyze your heart rhythm.

    So the antenna is at very bottom? With no shielding whatsoever giving your body a nice radiation boost?

    idmitriy - Reply

    • Time to dig into that second electrode—the all-new digital crown. We pull off some pieces and quickly find the fun parts.

    • Grab your magnifying glass—we're entering micro-world.

      • The internal golden cylinder has micro scratches on it, allowing an optical encoder (the little black box on the ribbon cable) to track its rotation.

      • The springy bracket behind the cylinder likely conducts the electrical signal from your finger through to the watch, completing the ECG circuit.

      • The tiny switch behind that spring acts as the crown's mechanical button. Plus, there's a nice gasket on the exterior crown shaft for ingress proofing.

    Would love to get more details on the ECG hardware. Did Apple use a piezo sensor or did they use a unique design?

    Wes - Reply

    How did you remove the digital crown?

    Kev - Reply

    • The original Apple Watch was revolutionary upon its release, but the yearly updates have been mostly minor—until now.

      • Where the first Watch was awkwardly layered together and used too much glue, the Series 4 feels much more thoughtfully laid out.

      • Apple pundit John Gruber has compared this to the leap in design brought by the iPhone 4, and we might even go a bit further and call it an iPhone 5: a device that knows its priorities, and wants to look as elegant inside as out.

    • If this watch didn't get your heart rate up, maybe it's time for a double iPhone teardown?

    • Big thanks to Creative Electron for helping out! Now only one thing remains. Drumroll please ...

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  4. Final Thoughts
    • Watch band replacements remain fast and simple, and are even backward-compatible with previous models.
    • Screen replacements are difficult but do-able—it's the first thing to come off, and detaches via simple ZIF connectors.
    • Battery replacements are pretty straightforward, once you're inside.
    • While not proprietary, incredibly tiny tri-point screws are a repair hinderance. And they are all over the place.
    • Several component flex cables are mounted directly to the S4 package, requiring skilled microsoldering to replace.
    • The resin-encased S4 system makes most board-level repairs impossible.
    Repairability Score
    Repairability 6 out of 10
    (10 is easiest to repair)


So how much of the inside is actually accessible and serviceable from the back of the device?

That looks a lot less hard to remove and put back without losing waterproofing (looks like it even has a silicone gasket…)

maarten - Reply

Besides the sensors attached to the bottom cover, it doesn’t look like you can get to the battery and other components from that side. The S4 blocks everything and it’s much too large to remove from the bottom out. Much of the screw heads are also facing away from the bottom side.

bert -

It is not possible to access the internals from the back, the back is locked to the case with screws from the inside.

Tom Chai -

%#*@ impressed with the new design

Yolo - Reply

Looks to me like the black pads would act as a shock absorber of sorts for the SiP to move against in a bang, sorta like jewel shock absorbers in mechanical watches.

tipoo - Reply

Any indication of how much ram the new GPS and cell modem models have?

ijuggle5 - Reply

wait, are you not opening up the SiP?

Suchir Kavi - Reply

It is resin encased, not very easy to do.

Dillan -

About the sensor from Bosch, it should be Bosch Sensortek if it is right. Sensortek is the company for consumer electronics, Bosch it self only sells sensors for automotive.

Zu deutsch:

Bei dem Sensor handelt es sich vermutlich tatsächlich um ein Produkt von Bosch. Allerdings verkauft Bosch selbst nur an Automotive Kunden und die Sensoren für Consumer kommen von der Tochtergesellschaft Bosch Sensortek. Einfach der vollständigkeit halber.

Ich habe für Bosch im Halbleiterwerk in Reutlingen gearbeitet und auch solche Chips im Bereich Lithographie bewegt.

TheLOD2010 - Reply

Is the diagnostic port 6 pins or 5 pins?

Jake - Reply

appears to be 6; the contacts are visible in the last picture below the speaker on the top left.

lteffertiller -

really cool teardown! if i can complain, maybe use a microfiber towel to remove fingerprints before taking the glorious money-shots. unless those were included for a sense of scale…?

Patrick Schoolcraft - Reply

Please disassemble the optical sensor which seems to be new, 6 LEDs and 8 photodiodes, please check for wavelength of LEDs (e.g. power them and check out the colors).


Franz Hohler - Reply

Yes, please do that! It’s very important to figure out how much better the sensor is. Thank you!

ps: I think it’s 4 LEDs

Annie B -

So just to confirm, the battery size is DOWN from 1.34 watt-hour of last year’s 42 mm watch to 1.12 watt-hour of this years 44 mm watch, is that the case here?

I’m not sure if the efficiency improvement in the S4 SiP compared to S3 of last year’s model would make up for that 20% battery loss and the 30% larger screen size. I would imagine the actual stand-by time would decrease by a fair margin compared to last year’s model (44 mm vs 42 mm).

saturnv - Reply

I must say I don’t mind the tri-point screws. At these sizes, phillips screws are a real pain - like they aren’t at any size, think on - dropping to just three wings gives the screw a bit more meat.

But then again, I have a similar argument for pentalobe - that screw size is too small for torx or hex, Phillips is bad and wrong - pentalobe makes a nice, solid joint between screw and driver.

Robert Backhaus - Reply

it should be noted that display replacements are not doable since apple changed something in watchOS 4.3.1 which pairs the display to the watch. Watches with swapped displays won’t pair to phones and also wont update…

darker - Reply

IFixit staff sure has a strange concept of that overall ‘repairability’ score. Based on the information I’ve seen, and the fact that you’ve permanently compromised the water proofing by opening the device and not replacing the adhesive pack with a new one that Apple won’t provide, I don’t see how this gets anything higher than a “3”. Looking at the pictures, there was also some pretty rippin’ adhesive in there, looking at the distortion on the battery envelope. 4 years ago, you would have crapped all over this thing.

SonarTech - Reply

It seems iFixit ALWAYS give better score to Apple stuff, even if they don’t open things (like on other manufacturer’s items) that tend to give *bad* score… is iFixt a *real* iThing like Apple funded? thus doing this?

jorgehpm - Reply

So the antenna is at very bottom? Giving your body a nice and radiation boost?

idmitriy - Reply

If you’re worried about the microscopic amount of radiation this thing puts out, then don’t eat any bananas; the potassium in them has more radiation.

ktappe -

Hi. Anybody know, is the Watch s4 case and screen of GPS version and LTE interchargeble or not? Thanks.

GeorgeF - Reply

Anybody knows what is the Sensor used to measure the rotation of the crown?

Cesar - Reply

It’s an optical rotary encoder—basically this sensor watches microscopic scratches on this cylinder and counts passing scratches as the crown turns to figure out when and how much it’s turning.

Adam O'Camb -

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