I did not see or hear any blindspot warning on the Model 3 I tested. And the mirrors are small.
You can pay extra for a computer to tell you what it thinks is in your blind spot and hope it's right and you interpret the signals correctly, or you can learn to use your side mirrors correctly to eliminate blind spots all together and see for yourself at a glance what it is actually all around you.
How To: Adjust Your Mirrors to Avoid Blind Spots
You're welcome.