Your phone shouldn't spy on you. Here's what stopping it costs

A phone knows more about you than anything else you own: where you sleep and work, who you talk to and when, what you search for, your health and money apps. By default, much of that leaves the phone. Apps embed advertising and analytics libraries, an advertising ID ties their reports together, location permissions granted once keep reporting in the background, and the operating system's own services send usage and location data to the platform vendor.

“I have nothing to hide” misses the point. Data collected for ads gets sold to data brokers, leaks in breaches, and is combined into profiles you never see and can't correct, which can shape the prices, insurance offers and job ads you're shown. Data that was never collected can't leak or be sold later.

The catch is that the modern app ecosystem is built on the same Google services that do much of the collecting. Payments, notifications, maps and app security checks all run through them. Step away from those services and the things built on them start to fail. That is the trade this guide is about.

Many banking apps check the phone with Google's Play Integrity API. Its stricter levels require a certified manufacturer image and a locked bootloader, which a custom ROM can't honestly provide. With no Play services at all, the check can't even run. Whether your bank's app works then depends on which level it demands, whether it also checks for root, and on your phone and ROM, and it can change with any app update. That's why CustomDroid doesn't claim that banking “works” on any ROM.

What people do about it:

• Check before you switch. Our banking app reports collect what readers have found, by ROM and Google setup, each with its date, and you can add your own. Bigger community lists: Plexus tracks app compatibility on de-Googled and microG phones, and PrivSec keeps a banking app list for GrapheneOS. They are other people's reports on a given date, not guarantees. Look at how recent the entry for your bank is.
• Use the bank's website. Most banks offer everything except tap-to-pay in the browser. Some need the app to approve logins or payments, so check that first.
• Pick a ROM that banks can verify. GrapheneOS runs with a locked bootloader and publishes a guide for app developers on accepting it through hardware attestation. Some banks do; most don't yet.
• Keep a second device, such as your old phone on stock software, for the one app that won't cooperate.

Tools that fake a passing integrity result exist. They can break with any update, and you'd be relying on one to reach your money. If an app is essential, find out before you wipe the phone. Don't count on a workaround afterwards.

There's no prize for reaching level 5. The honest picture:

• Levels 1 and 2 are worth it for nearly everyone. They remove most advertiser tracking and cost close to nothing.
• Level 3 makes sense if your phone no longer gets updates (see what end-of-life means), or if it's the platform itself you want to limit. If you own a Pixel, GrapheneOS with sandboxed Play gives up the least.
• Level 4 is for people who have checkedthat the apps they can't live without work there, or who have decided they can live without them.
• Going back is allowed. Most phones can return to stock firmware. A private-enough phone you keep using beats a perfect one you abandon after a month.

One caution on security. An unlocked bootloader protects you less against someone who physically has your phone. A few ROMs, GrapheneOS and CalyxOS among them, support relockingon specific phones. If a thief or a border search worries you more than advertisers do, that matters more than which level you're on.