If we had a choice, would any of us want to be tracked online for the sake of seeing more relevant digital ads?

We are about to find out.

On Monday, Apple plans to release iOS 14.5, one of its most anticipated software updates for iPhones and iPads in years. It includes a new privacy tool, called App Tracking Transparency, which could give us more control over how our data is shared.

Here’s how it works: When an app wants to follow our activities to share information with third parties such as advertisers, a window will show up on our Apple device to ask for our permission to do so. If we say no, the app must stop monitoring and sharing our data.

A pop-up window may sound like a minor design tweak, but it has thrown the online advertising industry into upheaval. Most notably, Facebook has gone on the warpath. Last year, the social network created a website and took out full-page ads in newspapers denouncing Apple’s privacy feature as harmful to small businesses.

A big motivator, of course, was that the privacy setting could hurt Facebook’s own business. If we choose not to let Facebook track us, it will be harder for the company to see what we are shopping for or doing inside other apps, which will make it more difficult for brands to target us with ads.(Mark Zuckerberg, Facebook’s chief executive, has disputed that his company’s business will be hurt by Apple’s policy.)

“This is a huge step in the right direction, if only because it’s making Facebook sweat,” said Gennie Gebhart, a director at the Electronic Frontier Foundation, a digital rights nonprofit.

But, she added, “One big question is, will it work?”

Ms. Gebhart and other privacy experts said Apple’s new feature might not be enough to put an end to shady tracking on iPhones. It could simply push developers and ad-technology firms to find loopholes so they can continue tracking people in different ways, she and others said.

For about two months, I have been testing early versions of iOS 14.5 to get acclimated with the new privacy control and other new features. Only a few developers have been testing the pop-up window with the public, so my findings about how well the privacy feature works have been limited.

But I found that iOS 14.5 also has other important new features. One is the ability to use Siri to work with a music player other than Apple Music, such as Spotify. That’s a big deal: In the past, you could only ask Siri to play songs through Apple Music, so the voice assistant wasn’t as useful for those who preferred other music services.

Here’s what you need to know about Apple’s new software.

Don’t Track Me (Please)

It’s important to understand how tracking works inside apps.

Let’s say you use a shopping app to browse for a blender. You look at a blender from Brand X, then close the app. Later, ads for that blender start showing up in other mobile apps, like Facebook and Instagram.

Here’s what happened: The shopping app hired an ad-tech company that embedded trackers inside the app. Those trackers looked at information on your device to pinpoint you. When you opened other apps working with the same ad-tech firm, those apps were able to identify you and serve you ads for Brand X’s blender.

Apple’s new privacy feature is intended to let you decide whether you want that to happen. Now, when you open some apps, you will be greeted with a pop-up window: “Allow [App Name] to track your activity across other companies’ apps and websites?” You can choose “Ask App Not to Track” or “Allow.”

When we select “Ask App Not to Track,” two things happen. The first is that Apple disables the app from using an Apple device identifier, a random string of letters and numbers assigned to our iPhones and that is used to track our activities across apps and websites. The second is that we communicate to the app developer that, broadly speaking, we don’t want our information to be tracked and shared with anyone in any way.

That seems easy enough. But No. 2 is where things also get slightly complicated.

Ad-tech companies already have many ways to follow us beyond Apple’s device identifier. For example, advertisers can use a method called fingerprinting. This involves looking at seemingly innocuous characteristics of your device — like the screen resolution, operating system version and model — and combining them to determine your identity and track you across different apps.

It’s difficult for Apple to block all tracking and fingerprinting happening on iPhones, privacy researchers said. That would require knowing about or predicting every new tracking method that an ad-tech firm comes up with.

“From a technical standpoint, there isn’t a whole lot that you can do” to stop such tracking, said Mike Audi, the founder of Tiki, an app that can help you see what other apps are doing with your data.

Yet the privacy change is still significant because it explicitly asks us for consent. If we tell apps that we don’t want to be tracked and they keep doing so, Apple can ban the offenders from its App Store.

The pop-up window also makes the privacy control far easier for people to discover, said Stephanie Nguyen, a research scientist who has studied user experience design and data privacy. In the past, iPhone owners could restrict advertisers from tracking them, but the tools to do so were buried in settings where most people wouldn’t look.

“The option was available before, but really, was it?” Ms. Nguyen said. “That’s a big shift — making it visible.”

As of this week, all apps with tracking behavior must include the App Tracking Transparency pop-up in their next software updates. That means we initially will probably see a small number of apps requesting permission to track us, with the number growing over time as more apps get updated.

Overdue Features

Apple’s new software also includes two other interesting new features: the ability to use Siri to play audio with a third-party app like Spotify and the option to quickly unlock an iPhone while wearing a mask.

For many, these will feel long overdue. Siri has generally worked only with Apple Music for music playback since 2015, which has been annoying and inconvenient for those who want to use the voice assistant to play songs using other music apps. The change comes as antitrust scrutiny mounts over whether Apple stifles competition by favoring its own apps.

To make Siri work with other audio services, you won’t have to change any settings. If you normally listen to music with a third-party app, such as Spotify, Siri will simply learn over time that you prefer that app and react accordingly. (Audio app developers need to program their apps to support Siri, so if they haven’t done so yet, this won’t work.) That means if you always use Spotify to play music, you will be able to say “Hey Siri, play The Beatles” to start playing a Beatles playlist on Spotify.

The other new feature helps solve a pandemic issue. For more than a year, wearing a mask has been extra annoying for owners of newer iPhones that have face scanners to unlock the device. That’s because the iPhone camera has not been able to recognize our covered mugs. Apple’s iOS 14.5 finally delivers a mechanism to unlock the phone while masked, though it requires wearing an Apple Watch.

Here’s how that works: When you scan your face and the phone determines it can’t recognize you because your mouth and nose are obstructed, it will check to see if your Apple Watch is unlocked and nearby. The Apple Watch, in effect, acts as proof to verify that you are the one trying to unlock your phone.

To make this work, update the software on your iPhone and Apple Watch, then open the Settings app on your iPhone. Scroll down to “Face ID & Passcode.” In this menu, go to “Unlock with Apple Watch” and toggle on the option to use your Apple Watch to unlock when the image scanner detects your face with a mask.

Next time you are at the grocery store and look at your phone, your watch will vibrate once and unlock your phone. Sweet relief.