The Apple Watch may be beautiful on the outside, but how about on the inside? In this Cracking Open installment, we go inside the watch’s case for a look at the hardware that powers Apple’s new wearable.

The Apple Watch comes in three different models, two different sizes, and six different finishes. There are more than a dozen different bands and prices range from $349 all the way up to ridiculous $17,000 for the gold versions.

Our test unit was a 42mm stainless steel model with a black sport band. It measured 42mm high, just under 36mm wide, 10.5mm thick. It weighed a very light 50 grams.

The front panel on this model is made from sapphire crystal, compared to Ion-X glass on the aluminum-bodied Sport model.

Along the right edge there’s the Digital Crown and Side button. On the back are the heart rate sensor, speaker, and microphone. There are also release buttons for each side of the band and a diagnostic port is hidden behind a small metal panel, which is visible only when you remove the band.

Now that we’ve looked at the outside of the Apple Watch, let’s get to the fun part and crack it open.

For more information on the 2015 Apple Watch, including real-world tests and pricing, check out Scott Stein’s full CNET review.

Cracking Open observations

Well-made device: The parts for the Apple Watch are well-built, the joints are tight, and the device feels solid.

Difficult (but not impossible) to open: To get inside the Apple Watch, you must remove the display. Unfortunately, the display is attached to the watch body with both adhesive and a physical snap. I loosened the adhesive by heating it and separated the display panel from the body with the help of an extremely thin knife. I then worked my way around the edges of the display with plastic tools, being careful not to damage any of the fragile cables under the display. You don’t need any special tools to get inside the Apple Watch, but you do need a lot of patience and a steady hand.

To see more photos of our Apple Watch (2015) teardown, check out our full cracking open gallery.

Tiny components: All the connectors and components inside the Apple Watch are extremely small. It is a watch after all.

Special tools required: There are several tiny tri-wing screws inside the Watch. You’ll need a set of precision tri-wing screwdrivers to remove them.

Some replaceable parts: Like most Apple products these days, the Watch wasn’t meant to be DiY serviceable. Some parts, such as the front panel and display assembly, Taptic Engine, speaker, and battery, can be removed and replaced without damaging the other components. And, I suspect it won’t be long before broken screens can be replaced at the Apple Store.

Unfortunately, removing parts buried deeper within the metal body (such as the S1 SiP and heart rate sensor) is not so simple. I’m sure Apple technicians can replace the entire internal workings of a watch. (They’d have to for customers who forked over $15,000 for an Apple Watch Edition.) But if the S1 system in package (SiP) gets damaged (as unlikely as that might be), I wouldn’t count on replacing it yourself.

Packed with cool tech: Apple used a lot of unique hardware inside the Watch. For example, the processor, much of the system board, and most of the other ICs are completely covered in a molding compound. I’ve never seen so many separate components encapsulated like this. And thanks to the analysis of companies such as Chipworks, we know that the Apple Watch has a new STMicroelectronics 6-axis gyroscope in it, as well as at least 30 components mounted to the S1 SiP (which measures a mere 26mm x 28mm).

Not practical to upgrade: Unfortunately, there’s no way to upgrade the 2015 Apple Watch, without completely replacing all the Watch’s internal hardware–a very impractical process. If Apple does release a new Watch next year, I’m doubtful that it will have the same body as this year’s Watch. So, it’s unlikely the hardware from a 2016 Watch would fit in the body of the 2015 model. When the new models come out next year (if they do), the old one will just be outdated.