Theft deterrent system light: always on when ignition is off

My Prius (w/ roughly 51,000 km) has the Smart Key System (SKS). According to the owners manual (corroborated by my experience), the indicator light for the theft deterrent system should not come on until a) the ignition is turned off and b) the driver's door is opened.

As of yesterday morning, the indicator light has started to flash as soon as the ignition is turned off (i.e., without the driver's door being opened). The light continues to flash until the ignition is turned on. I noticed that when I exit the car and press the exterior lock button, the indicator light stays on for several seconds, and then resumes flashing.

Coincidently, when I started the car yesterday morning (when it was about -20C), the high temperature warning light (which has never been on before) came on for a few seconds. I don't recall whether that light went out before or after the ICE started). That light has not come on since.

I phoned my dealer's service department and was told that the issue with theft deterrent system light is not critical. They'll check it out at the next scheduled service. However, if the temperature warning light should come on again, I should bring the car in right away.

Any ideas about why the theft deterrent system light now starts to flash as soon as the ignition is turned off?

 

I've owned the Prius for 2.5 years, and I'll swear on a stack of Haynes manuals that until yesterday, the theft deterrent system indicator never came on if the ignition was off and the Smart key was in the car. Similarly, unlocking the door (from the outside) used to turn off the indicator; now the indicator continues to flash until the ignition is on.

It's not just my imagination that the theft deterrent system is behaving differently than in the past.

 

Laugh, and the world laughs with you, question the operation of the theft deterrent system (TDS) indicator, and .......

Logically, the purpose of the indicator light is show whether or not the TDS is active. If the indicator light flashes even when the car is unlocked (as it nows does), you can get a "false positive" reading (i.e., the TDS appears to be activated when it actually has not been). That seems to defeat the purpose of having an indicator in the first place.

 

It seems to me that the TDS indicator should only flash when the car is locked. Suppose a) that you mistakenly think you've locked the car because the indicator is flashing, and b) a potential thief doesn't notice the flashing indicator and tries to open the door. The result is obvious: the thief gets into your car.

 

Yes, the TDS is not a fulfledged alarm. However, the manual for my 06 states that the TDS is supposed to make the headlights flash and the horn honk if a locked door is opened (or the battery is disconnected) when the SmartKey is not present.

I can verify from personal experience that if a thief breaks a window and reaches into the car w/o unlocking the door, the TDS ignores the intrusion.