Dashboard dimple

[ajstars]

My Avensis had one, my Rav4 has one and both my Surfs have one. What is the round smoked plastic dimple on the offside top of the dashboard close to the windscreen? There is a small chip or sensor or something under the cap.
I read elsewhere it is for auto dimming lights - clearly not! Is this part of the key remote sensor maybe?
Just seen that it is definitely wired up with two wires so it does something!