The response to your query is "no" There are no simple techniques. You may find the information here if you want additional details:
- How to get device make and model on iOS?
 
and
- how to check screen size of iphone 4 and iphone 5 programmatically in swift
 
The iPhone X height is 2436 px
From Device Screen Sizes and resolutions:
From Device Screen Sizes and Orientations:
Swift 3 and later:
if UIDevice().userInterfaceIdiom == .phone {
    switch UIScreen.main.nativeBounds.height {
        case 1136:
            print("iPhone 5 or 5S or 5C")
        
        case 1334:
            print("iPhone 6/6S/7/8")
        
        case 1920, 2208:
            print("iPhone 6+/6S+/7+/8+")
        
        case 2436:
            print("iPhone X/XS/11 Pro")
        
        case 2688:
            print("iPhone XS Max/11 Pro Max")
        
        case 1792:
            print("iPhone XR/ 11 ")
        
        default:
            print("Unknown")
        }
    }
Objective-C:
if([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        switch ((int)[[UIScreen mainScreen] nativeBounds].size.height) {
            case 1136:
                printf("iPhone 5 or 5S or 5C");
                    break;
            case 1334:
                printf("iPhone 6/6S/7/8");
                break;
            case 1920:
            case 2208:
                printf("iPhone 6+/6S+/7+/8+");
                break;
           case 2436:
                printf("iPhone X/XS/11 Pro");
                 break;
            case 2688:
                printf("iPhone XS Max/11 Pro Max");
                 break;
            case 1792:
                printf("iPhone XR/ 11 ");
                 break;
            default:
                printf("Unknown");
                break;
        }
    }
Xamarin.iOS:
if (UIDevice.CurrentDevice.UserInterfaceIdiom == UIUserInterfaceIdiom.Phone) {
    if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 1136) {
        Console.WriteLine("iPhone 5 or 5S or 5C");
    } else if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 1334) {
        Console.WriteLine("iPhone 6/6S/7/8");
    } else if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 1920 || (UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 2208) {
        Console.WriteLine("iPhone 6+/6S+/7+/8+");
    } else if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 2436) {
        Console.WriteLine("iPhone X, XS, 11 Pro");
    } else if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 2688) {
        Console.WriteLine("iPhone XS Max, 11 Pro Max");
    } else if ((UIScreen.MainScreen.Bounds.Height * UIScreen.MainScreen.Scale) == 1792) {
        Console.WriteLine("iPhone XR, 11");
    } else {
        Console.WriteLine("Unknown");
    }
}
Based on your question as follow:
Or use screenSize.height as float 812.0f not int 812.
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) {
    CGSize screenSize = [[UIScreen mainScreen] bounds].size;
        // 812.0 on iPhone X, XS
        // 896.0 on iPhone XS Max, XR.
    if (screenSize.height >= 812.0f)
        NSLog(@"iPhone X");
    }
For more information you can refer the following page in iOS Human Interface Guidelines:
- Adaptivity and Layout - Visual Design - iOS - Human Interface Guidelines
 
Swift:
Detect with topNotch:
If anyone considering using notch to detect iPhoneX, mind that on "landscape" its same for all iPhones.
var hasTopNotch: Bool {
    if #available(iOS 13.0,  *) {
        return UIApplication.shared.windows.filter {$0.isKeyWindow}.first?.safeAreaInsets.top ?? 0 > 20
    }else{
     return UIApplication.shared.delegate?.window??.safeAreaInsets.top ?? 0 > 20
    }
    return false
}
Objective-C:
- (BOOL)hasTopNotch {
   if (@available(iOS 13.0, *)) {
       return [self keyWindow].safeAreaInsets.top > 20.0;
   }else{
       return [[[UIApplication sharedApplication] delegate] window].safeAreaInsets.top > 20.0;
   }
   return  NO;
}
- (UIWindow*)keyWindow {
    UIWindow        *foundWindow = nil;
    NSArray         *windows = [[UIApplication sharedApplication]windows];
    for (UIWindow   *window in windows) {
        if (window.isKeyWindow) {
            foundWindow = window;
            break;
        }
    }
    return foundWindow;
}