blinking dim red keyfob light

Sorry, if this was covered before, I searched but found nothing.
I was playing with Torque App last night and noticed dim red blinking keyfob light while inside the car that was in "diagnostic" mode (non-ready, but everything on). It blinked only several times and I only noticed it because the keys were on the passenger seat. I usually keep them in my pocket and don't see anything. The light is above the lock button and it's not marked.

Is this a normal function or low battery alert? The car is 2 years old.

This smart key guide makes no mention of it: Toyota Prius Smart Key - Battery Change & Lost Key Replacement Tips