Differentiate between screen lock and home button press on iOS7

This can help you both on iOS6 & iOS7 :).

When user press lock button you will get a com.apple.springboard.lockcomplete notification.

//new way
//put this in - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
                                    NULL,
                                    displayStatusChanged,
                                    CFSTR("com.apple.springboard.lockcomplete"),
                                    NULL,
                                    CFNotificationSuspensionBehaviorDeliverImmediately);

//put this function in AppDelegate
static void displayStatusChanged(CFNotificationCenterRef center,
                                 void *observer,
                                 CFStringRef name,
                                 const void *object,
                                 CFDictionaryRef userInfo) {
    if (name == CFSTR("com.apple.springboard.lockcomplete")) {
        [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"kDisplayStatusLocked"];
        [[NSUserDefaults standardUserDefaults] synchronize];
    }
}

//put this in onAppEnterBackground
UIApplicationState state = [[UIApplication sharedApplication] applicationState];
    if (state == UIApplicationStateInactive) {
        NSLog(@"Sent to background by locking screen");
    } else if (state == UIApplicationStateBackground) {
        if (![[NSUserDefaults standardUserDefaults] boolForKey:@"kDisplayStatusLocked"]) {
            NSLog(@"Sent to background by home button/switching to other app");
        } else {
            NSLog(@"Sent to background by locking screen");
        }
    }

//put this in - (void)applicationWillEnterForeground:(UIApplication *)application
[[NSUserDefaults standardUserDefaults] setBool:NO forKey:@"kDisplayStatusLocked"];
[[NSUserDefaults standardUserDefaults] synchronize];

CGFloat screenBrightness = [[UIScreen mainScreen] brightness];

NSLog(@"Screen brightness: %f", screenBrightness);

UIApplicationState state = [[UIApplication sharedApplication] applicationState];

if (state == UIApplicationStateInactive) {

    NSLog(@"Sent to background by locking screen");

} else if (state == UIApplicationStateBackground) {
    if (screenBrightness > 0.0) {
        NSLog(@"Sent to background by home button/switching to other app");
    } else {
        NSLog(@"Sent to background by locking screen");
    }
}