How can I base take input based on my device type?

I believe I can check to see if I am on a mobile device by using:

if (SystemInfo.deviceType == DeviceType.Handheld)
{

}

But if that is the case, I want to disable:

private void OnMouseDown()
{

}

and use something appropriate for mobile such as:

private void Update()
{
    if (Input.GetTouch() > 0)
    {

    }
}

I need to do this because OnMouseDown() will still be called on mobile, but it is recommended to not be used.

How can I call OnMouseDown() if I am on a desktop, and call Input.GetTouch() > 0 if I am on a mobile?

Just check at the very beginning of OnMouseDown() and return right away if it is a mobile device.

private void OnMouseDown()
{
    if (SystemInfo.deviceType == DeviceType.Handheld)
    {
        // Exit Method
        return;
    }
    // Not a handheld continue with Non-Handheld code...
}