What is a UDID?
UDID stands for Unique Device Identifier — a unique string assigned by Apple to every iOS and iPadOS device. Think of it as your device's serial number for software purposes: globally unique and permanent.
A modern UDID looks like this:
00008110-001A2B3C4D5E6F78
The current format (iOS 11+) is 25 characters in 8-16 format. The legacy format is a 40-character hexadecimal string.
What is a UDID Used For?
1. Installing Beta / Ad Hoc Apps
Apple's Ad Hoc distribution requires developers to register a tester's UDID in their Apple Developer account before sending them an app. This is the most common reason someone asks for your UDID.
2. Device Registration
Each Apple Developer account can register up to 100 devices per year. Developers collect UDIDs from testers and add them to their developer portal before building a Provisioning Profile that includes those devices.
3. Enterprise App Distribution
Some enterprise distribution platforms collect UDIDs for device management and usage analytics, even when Apple's standard enterprise certificate doesn't strictly require it.
4. Crash Log Symbolication
Xcode crash reports include the UDID, allowing developers to map a crash to a specific test device for precise reproduction.
UDID vs. Other Device Identifiers
| Identifier | Full Name | Key Characteristic |
|---|---|---|
| UDID | Unique Device Identifier | Device-level, permanent, survives restores |
| IDFA | Identifier for Advertisers | Used for ad targeting, user-resettable |
| IDFV | Identifier for Vendor | Shared across one developer's apps, resets on uninstall |
| Serial Number | Serial Number | Hardware ID for warranty and repairs |
The key distinction: Serial Number = hardware tracking; UDID = software development and testing.
Privacy Considerations
Since iOS 5, Apple has blocked third-party apps from reading device UDIDs directly via code. The only legitimate ways to obtain a UDID today are:
- Via Xcode on a Mac (requires a computer and cable)
- Via Apple's OTA Profile Service protocol (what UDID.my uses — no computer needed)
UDID.my uses Apple's official Profile Service mechanism, where iOS itself reports the device information. The process is transparent: you review and approve each step.
How to Find Your UDID
The easiest way: use UDID.my on your iPhone or iPad — no computer, no cables, done in 30 seconds.
For step-by-step instructions, see: How to Get Your iPhone / iPad UDID Without a Computer