Incessant beeping cured (maybe) by battery reset

My question is less about the noise than the so-far unfindable source. My 2014 Prius with 102k miles started beeping a few days back, incessantly — every 3 seconds whether the car was running or turned off and locked up. After it beeped during shutdown overnight I tested the 12v battery. It tested fine. A scanner seemed to find no codes, though i will see if Dr. Prius finds anything. The beeping did not trigger any warning lights. However, the imobilizer system light flashed per normal and it seems to flash at the same 3 second interval as the beeps.

The beeping finally stopped after a 15-20 minute period with the negative terminal off the 12v battery. Given my automotive luck, the beep will probably return.

Suspects range from a faulty door or hatch microswitch to (maybe) a failed or failing front passenger airbag sensor in that seat. My disabled wife is horribly obese from her ailment and at times the air bag ‘on’ light fails to illuminate, though it will light up for smaller individuals.

Any thoughts as to the source/cause/potential code of the mystery beeps?

Otherwise, the traction battery is down to about 60% capacity, the mileage is down and I’m entertaining thoughts of trading it next year or dumping maybe $4k into it for a replacement battery, new water pumps and plugs and driving it two or three more years. It’s our runabout car and gets about 7-8k a year. I have a big, beautiful, 2003 Jaguar Vanden Plas for fun.

Eliot/Northern VA

 

Fortunately the noise is at least for now silenced. While driving, I thought the beep was behind me. While parked at home, I thought it was perhaps under the dash in the “which smoke detector is it” mode. It definitely was not under the hood.

If the little basta….I mean darling rears its ugly head again I’ll try to see if i can narrow it down a bit.

Thanks.

Eliot

 

PROBLEM FOUND. Sorry I cannot find how to edit the original post or change the heading to say SOLVED.

It was a failing battery in a toll lane transponder. New units ordered for both cars. Tip off was mentioning it to a friend who said they had the same issue, ultimately traced to aging battery in transponder. For grins enroute to pickup lunch I pulled the transponder off the windshield and moved the switch to trigger the HOV/carpool function. The device immediately began beeping and is now locked in the trunk until the new ones arrived. They told me it was OK to swap the one functioning unit between cars.

Thanks to all who chimed in (pun slightly intended), and I wanted to close out the matter.

Cheers.