What is this black sensor thing on my Mazda 3?
 

Hi guys and girls,

so I installed a reverse camera, and to do so I removed my number plate and found a black bar (back and under the plate light)
its wired up too (unsure where its going) I was wondering if anyone knows what this is?

See image attached
https://cimg8.ibsrv.net/gimg/www.maz...1ee8f9daa4.jpg

It's to do with the keyless entry system.