Introduction

On iOS, there is no general-purpose permanent device ID that third-party apps are supposed to use the way older platforms exposed hardware identifiers. The right answer depends on what “unique” means in your app: vendor-scoped identity, advertising identity, or an app-generated identifier that you persist yourself.

Use identifierForVendor for Vendor-Scoped Identity

The most common built-in answer is identifierForVendor.

1import UIKit
2
3if let id = UIDevice.current.identifierForVendor?.uuidString {
4    print(id)
5}

This identifier is stable for apps from the same vendor on the device, but it is not a global immutable hardware serial number. That is an intentional privacy boundary.

It is usually appropriate when apps from the same developer need a shared vendor-scoped identifier.

Use Your Own UUID for App Identity

If what you really need is “an ID for this app installation,” generate your own UUID and store it persistently.

1import Foundation
2
3let installID = UUID().uuidString
4print(installID)

The usual next step is storing that UUID somewhere persistent, often the Keychain if you want it to survive ordinary app reinstalls more reliably than UserDefaults.

This approach is often better than trying to treat the device itself as the identity source.

Persist Generated IDs Carefully

Where you store the generated identifier changes its behavior. UserDefaults is simple, but it is tied more directly to the app’s local storage lifecycle. A Keychain-backed identifier is often chosen when the app wants a more durable installation identity.

That design decision matters more than the UUID generation itself.

Do Not Treat IDFA as a General Device ID

The advertising identifier exists for advertising-related use cases and is not the default answer for normal application identity. It has privacy and consent implications and should not be used casually as a substitute for an app-level identifier.

A good rule is:

• use vendor-scoped ID if vendor identity is what you need
• use your own generated UUID if app identity is what you need
• do not chase a hidden permanent device ID that iOS is intentionally not exposing

Remember That Uniqueness Is Only Part of the Design

A client-side identifier can help correlate an installation, but it should not be the whole security or identity strategy. Account-based identity, server-issued tokens, and backend validation are still the core tools for anything security-sensitive.

That is why the “best unique device ID” is often only one small part of the overall design.

Choose Based on the Real Requirement

Different goals imply different identifiers:

• analytics for one app installation: generated UUID
• coordination across the same vendor’s apps: identifierForVendor
• advertising workflows: advertising identifier with the right policy constraints

If the requirement is fraud detection or account tracking, the correct solution is often server-side account identity plus device signals, not a single magic device ID.

Common Pitfalls

• Looking for a permanent hardware-style device ID that iOS no longer intends third-party apps to use.
• Using identifierForVendor without understanding that it is vendor-scoped, not globally device-scoped.
• Treating the advertising identifier as a normal application identity mechanism.
• Storing a generated UUID in a place that does not match the persistence behavior you actually need.
• Designing security or account systems around one client-side identifier alone.

Summary

• iOS does not provide a general permanent device ID for normal app use.
• 'identifierForVendor is the usual built-in vendor-scoped identifier.'
• A generated UUID is often the best answer for app-specific identity.
• Persistence strategy matters as much as UUID generation.
• Choose the identifier type based on the real product requirement, not on the hope of a universal hardware ID.