Red lens on the back of WD5000BEVT

My laptop HDD (WD5000BEVT) failed so I replaced it. Does anyone know what this red lens on the back of the drive is for? It isn’t present on the new drive (entirely different series/model).

That is more likely to be some sort of sensor than a lens.

I will  research on this one and reply once we have the information.

Awesome! Thanks.

Looks more like an LED than a lens.