Panic mode

Recently my wife and I were sitting in our house and heard a loud horn going on and off repeatedly outside. We looked out the window and her Prius was flashing its lights and honking its horn repeatedly. I'm not up on all the technology, so I simply call this the car's panic mode. The car was locked at the time. We are both quite sure we didn't hit the red button in either of our key fobs, and, besides, I later tested the panic button on my fob from a room closer to the Prius than the one we were in when the noise started and it didn't activate the horn-honking.

From what little I have learned since then the two main things that would activate panic mode on the vehicle would be pushing the panic button or if someone were trying to break in to the car. The second cause is a real concern as it is disturbing to think someone would be trying to steal it out of our driveway. We went right out to the car and did not see anyone or anything suspicious and the car does not appear to have been harmed in any way.

My question is, is there any other way to put the car into panic mode? Could someone be driving by, operating an electonic device (garage door opener, radio, communication device, etc.) and trigger panic mode in our car by crossing radio or other electronic waves by accident? Are there other cases of this?? What are other causes for the car to go into panic mode?

I'd appreciate any info. anyone has on this issue.