Today, with an update to watchOS, Apple is making its electrocardiogram (EKG) reading feature available to Apple Watch Series 4 owners. It’s also releasing an irregular rate notification feature that will be available on Apple Watches going back to Series 1. Both are a part of watchOS 5.1.2.

When the Apple Watch Series 4 was announced this past September, the most significant new hardware feature besides the larger screen was probably the ability to take an EKG directly on the Watch. And while the electrodes on the digital crown and the backside of the Watch were there, the software to support them hadn’t been released. Now it’s here.

To take an EKG, you open up the EKG app on the Watch and lightly rest your index finger on the crown for 30 seconds. The Watch then acts like a single-lead EKG to read your heart rhythm and record it into the Health app on your phone. From there, you can create a PDF report to send to your doctor.

The Apple Watch is moving from fitness tracker to health monitor

The irregular heart rate monitoring is passive. Apple says that it checks your rhythm every two hours or so (depending on whether you’re stationary or not), and if there are five consecutive readings that seem abnormal, it will alert you and suggest you reach out to a doctor. If you have been previously diagnosed with atrial fibrillation, Apple’s setup process tells you not to use the feature.

Apple tells me these features are most definitely not diagnostic tools. In fact, before you can activate either of them, you will need to page through several screens of information that try to put their use into context and warn you to contact your doctor if needed. They are also not the sort of features Apple expects users to really use on a regular basis. The EKG feature, in particular, should only really be used if you feel something abnormal going on, and then you should only share the resulting report with your doctor, not act on it directly.

I wanted to get those caveats stated clearly. Firstly, because they’re important — don’t assume the Apple Watch can replace talking to a doctor, and don’t try to self-diagnose with it — and secondly, because these caveats can help put you in the right frame of mind for understanding how the Apple Watch is changing and how entering this new health space is neither simple nor easy.

Apple has received “de novo” clearance from the FDA for these features, which are a first for a consumer product you can buy directly. But one example of how this new use of technology is complicated is that FDA “clearance” is not the same thing as FDA “approval,” as Angela Chen has explained:

The Apple Watch is in Class II. For Class II and Class I, the FDA doesn’t give “approval,” it just gives clearance. Class I and Class II products are lower-risk products — as [Jon Speer, co-founder of Greenlight Guru] puts it, a classic Class I example is something like a tongue depressor — and it’s much easier to get clearance than approval.

Most people think of the Apple Watch as a fitness tracking device, but increasingly, it is becoming a health monitoring device — especially the Series 4. Along with the new EKG feature, it can also detect if its wearer suddenly falls to the ground. And all Apple Watches Series 1 and up can now keep an eye out for irregular and abnormally low or high heart rates.

But in this new kind of gadget world, understanding what a health monitoring device can and can’t do is essential. It can detect those things and that is genuinely good, but it doesn’t necessarily mean that it will, nor that you should depend on it to do so. It’s more of a backstop — or another source of data you can provide to your doctor.

With the EKG feature, that extra data could prove valuable. Apple says that having a potential EKG monitor on your wrist at all times means that you can get a reading at the moment you’re feeling your heart race, for example, instead of just describing it to your doctor later. But the risk is that people might not use that data properly (e.g., they might use it for self-diagnosis).

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Apple’s onboarding experience goes some way toward keeping you from falling into that trap. For both features, you’ll need to tap through several screens of information about atrial fibrillation and other heart issues. The design of that screen flow encourages actually reading about what you’re turning on, too, instead of just scrolling by and hitting accept like you do with the iTunes terms of service. There are specific animations, graphics, and pauses that feel like they’re designed to encourage users to pay attention.

I tried the EKG feature a couple of times, but, since I am not a doctor, I can’t tell you how accurate it is. One thing I could not test (thankfully) was the irregular heartbeat notification. There again, Apple is trying to be super clear that you should reach out to a doctor rather than act on the notification directly.

Both features are limited to the US for now, and they should be available today as part of the watchOS 5.1.2 update.