Warning light on dashboard

That's the tire pressure warning light. If the pressures are correct,
then you probably have dieing batteries for the monitors.

 

It's telling you that one (or more) tire pressure is low. If you've recently verified that in fact al four tires are properly inflated, then the sensor has probably gone haywire. Talk to your favorite Prius mechanic.

 

or ignore it

 

When it does that, it's not telling you about pressure in any tire. It's telling you it doesn't know the pressure in at least one tire, because of a system issue.

The system issue, at this age, tends to be that the battery has pooped out in one of the in-tire pressure transmitters.

 

Or...it could be that due to cold weather, the sensor is not reading the correct pressure. Have there been any temperature changes recently "in your neck of the woods"? You can put nitrogen in your tires at Costco for free (if you're a member) and this tends to help. Otherwise, it's probably a sensor gone bad if your pressure is accurate.

 

The TPMS computer chose to blink the light before going solid, so we know it is a system issue (most likely a dead transmitter), and not a pressure reading.