Identify iOS devices by a unique identifier (works on latest iOS version)

UIDevice+Extensions.h

#import <UIKit/UIKit.h>
#include <dlfcn.h>

static const CFStringRef kMGDieID = CFSTR("DieId");

@interface UIDevice (Extensions)

- (NSString *)dieID;
- (NSString *)batteryID;

@end

UIDevice+Extensions.m

#import "UIDevice+Extensions.h"

@implementation UIDevice (Extensions)

- (NSString *)dieID {
    void *libMobileGestalt = dlopen("/usr/lib/libMobileGestalt.dylib", RTLD_LAZY);
    NSParameterAssert(libMobileGestalt);
    CFStringRef (*MGCopyAnswer)(CFStringRef string) = dlsym(libMobileGestalt, "MGCopyAnswer");
    NSParameterAssert(MGCopyAnswer);
    CFStringRef dieID = MGCopyAnswer(kMGDieID);
    NSString *dieIDString = (__bridge NSString *)dieID;
    CFRelease(dieID);
    dlclose(libMobileGestalt);
    return dieIDString;
}

/* Only available on iOS 8+ */
- (NSString *)batteryID {
    void *IOKit = dlopen("/System/Library/Frameworks/IOKit.framework/Versions/A/IOKit", RTLD_LAZY);
    NSParameterAssert(IOKit);
    
    mach_port_t *kIOMasterPortDefault = dlsym(IOKit, "kIOMasterPortDefault");
    NSParameterAssert(kIOMasterPortDefault);
    CFMutableDictionaryRef (*IOServiceNameMatching)(const char *name) = dlsym(IOKit, "IOServiceNameMatching");
    NSParameterAssert(IOServiceNameMatching);
    mach_port_t (*IOServiceGetMatchingService)(mach_port_t masterPort, CFDictionaryRef matching) = dlsym(IOKit, "IOServiceGetMatchingService");
    NSParameterAssert(IOServiceGetMatchingService);
    kern_return_t (*IORegistryEntryCreateCFProperties)(mach_port_t entry, CFMutableDictionaryRef *properties, CFAllocatorRef allocator, UInt32 options) = dlsym(IOKit, "IORegistryEntryCreateCFProperties");
    NSParameterAssert(IORegistryEntryCreateCFProperties);
    kern_return_t (*IOObjectRelease)(mach_port_t object) = dlsym(IOKit, "IOObjectRelease");
    NSParameterAssert(IOObjectRelease);
    
    CFMutableDictionaryRef properties = NULL;
    
    mach_port_t service = IOServiceGetMatchingService(*kIOMasterPortDefault, IOServiceNameMatching("charger"));
    IORegistryEntryCreateCFProperties(service, &properties, kCFAllocatorDefault, 0);
    
    IOObjectRelease(service);
    
    NSDictionary *dictionary = (__bridge NSDictionary *)properties;
    NSData *batteryIDData = [dictionary objectForKey:@"battery-id"];
    
    CFRelease(properties);
    properties = NULL;

    dlclose(IOKit);
    
    return [NSString stringWithUTF8String:[batteryIDData bytes]];
}

@end