The horn started beeping loudly

That loud beeping would be the alarm being activated. Evidently the 'soul' that set it off had already departed by the time you got out to look. Seems like maybe the alarm actually worked. Either that or it was a false alarm, in which case you need to take it into the dealer to be checked.

 

Alarms aren't standard equipment on the GEN III. My IV doesn't have one. Does the car have an alarm system, such as the VIP RS3200 from Toyota?

 

in Subaru land they sell perimeter alarms. basically a shock sensor. the have two settings. most people use the lowest setting because the highest sensitivity setting sets the car off frequently.

if you have the VIP alarm maybe it has a lower setting???

 

Then it does not likely have an alarm system if one was not added by your dealer.
What happens if you go sit in the car and turn it on? Do you get any message on the display?

This is the only thing that seems even close from the manual:

(The horn will sound externally continuously when)

When the “POWER”
switch is in ON mode or
ACCESSORY mode, the
driver’s door was closed
after the key was carried
outside the vehicle, and
the shift position not in “P”

 

Please read that section in your Owner's Manual again. The horn does not sound in this situation - only the external buzzer.

It is possible that you are experiencing the same problem I noticed with my 2004 Prius. I always keep the key fob in my pants pocket. Apparently, I was lying on the couch in some position where the panic alarm button got pressed, which caused the horn to beep continuously.

If the key fob wasn't any place where the panic alarm button could have been pressed, I would have your car checked by the dealer.

 

I meant external alarm, which I assumed he may have meant when he said horn. Just trying to scrape for anything to help.

 

That red button is the panic button. For the Prius you have to press and hold it for about a second to set it off. Try it in different places around your house to see if it's possible that was the cause. Mine can set off the alarm with in the back corner office in the house.

It hasn't happened yet with my Prius but with my Windstar, it would happen frequently when my kids would sit on my lap to be read to and accidentally press the button while in my pocket.

BTW, I have the package 2 also.

Michael

 

That's the "Panic Alarm." You can hit that to sound the horn. While it sounds the horn, there's no relationship to a traditional theft alarm. I've set it off getting out of the car, when my pocket with the fob presses against the side of the car.

 

It blows until you hit the button again, as far as I know. Usually scares the crap out of me and reverberates in my garage, so I quickly grab the fob and hit it again to stop it.

 

yes, no.

 

The panic button will continuously sound the horn at any time. It doesn't matter when you left the car. I am sure there is a range limit, but I don't know what it is.

The first time I noticed this "problem", I was watching TV in my living room. I heard what sounded like a car alarm going off (i.e. a horn beeping continuously). Since it sounded nearby, I walked towards the front of the house and realized the sound was coming from my garage. I had no idea why the car was beeping. I then thought about the panic alarm, got the key fob out of my pocket and pressed the panic button, which silenced the horn.

The next time it happened, I knew what it was and how to stop it. What mystified me was the fact that I had the car for five years before this problem started. I haven't changed my habits, so I don't know why the I was suddenly triggering the panic alarm.

 

It's nothing. My gen two prius touring did that. And other cars in my neighborhood. Sometimes it had to deal with the temperature or something like that. Cause my dads old jeep grand charokee do that and we called the dealer and that's what they said. But when my neighbors car did that. It was because there battery was going dead.

 

Years ago I left my FOB (not a Prius) on the counter and my cat laid on it in the middle of the night and set it off.

Having the FOBS in one pants pockets and bumping it or relaxing on the couch and rolling over onto it..... are a frequent cause though and have been for years.