Red Key FOB light on dashboard slow blinking?

Please forgive me, this is my wife's car. I barely if ever drive it:

She drove the 2004 Prius, parked it. Shut it down. A Red very slow flashing light on the dash of a car/and key appeared. She claims she never seen this before.

She got out of the car, closed the doors.. and peeked in and again the flashing symbol was there.
She was concerned the car wouldn't start, she unlocked the doors, started the car... red flash went away... stopped the car... flash came back. Soon, I will to go outside to see if that red light is still blinking when she gets home.

I am pretty sure its the generic security system of the car, or the car cant find the key fob in the cab.. so its flashing .. i.e. that battery in the fob is not as powerful.

but I would like to confirm this is normal for the prius.. before she gets locked out of the car on a cold night.

I dont see any battery info regarding the key Fob in the manual. I sure as heck, dont want to go to the dealership for this issue.

I already instructed her about the key in the fob for the doors, and holding the fob to the start button if that ever happens. We never if ever stick the Fob into the dashboard slot. The keys are usually in a coat pocket, purse.

Thanks. I apologize in advance if this is a silly, harmless observation. I dont drive her car.

 

I have no idea what SKS entry means.. but yes you can walk up to the car and not touch the keyfob and the doors will recognize the keyfob in her pocket and unlock the doors. Optional, is putting the keyfob in the dash to start the car.
She does step on the brake pedal to start the car... no issue there.
She gets out of the car (stops it, etc) ... the red key fob starts flashing.
She comes back... the red key fob is still flashing. I am pretty sure its the security system.