DeviceModel.swift

extension UIDevice {
    var iPhone: Bool {
        return UIDevice().userInterfaceIdiom == .Phone
    }
    enum ScreenType: String {
        case iPhone4
        case iPhone5
        case iPhone6
        case iPhone6Plus
        case Unknown
    }
    var screenType: ScreenType? {
        guard iPhone else { return nil }
        switch UIScreen.mainScreen().nativeBounds.height {
        case 960:
            return .iPhone4
        case 1136:
           return .iPhone5
        case 1334:
            return .iPhone6
        case 2208:
           return .iPhone6Plus
        default:
           return nil
        }
    }
}

print(UIDevice().screenType)
//source: http://stackoverflow.com/questions/27775779/how-to-check-screen-size-of-iphone-4-and-iphone-5-programmatically-in-swift