Crazy possessed alarm!

[StellaArtois86]

Hello!

Newbie here. So we have a 2010 Prius. No issues with it so far. New Battery 18 months ago. Based in Scotland, UK. 

In the last few months, the alarms been going off randomly. Usually at night, of course, because we live on a quiet street 

Today my husband took it into Toyota for a diagnostics test. They found a faulty motion sensor so removed that. They cleaned the hood latch in case it was that. They said they disconnected the horn so it shouldn’t make a sound if it went off again. Husband bought it home. Left it unlocked. Just Incase. He went off to a conference an hour ago. I locked it. It went off, blaring horn, indicators flashing. Rang Toyota, they’re stumped. They’ve disconnected the horn as a precaution until I can take it back in on a Tuesday. Help!!!

[lovec1990]

better hire exorcist this is beyond Toyota mechanics😁.

You said they disconnected the horn so how does blaring horn ocure unless they did not disconnect horn?

 

[StellaArtois86]

No one has any idea!! So they said they disconnected it when my husband took it in but it went off anyway when he got home. So took it back in last night and they disconnected the front horn this morning. Wasn’t aware there was more than one!

[Mick F]

We bought a brand new Clio in 2001.

The alarm would go off every night.  No-one near it, nothing touched, but it would go off every single night.  Good job we're a long way off any neighbours!

Finally traced it down to a moth setting off the alarm as it fluttered around inside by the light of the moon!

Renault decreased the sensitivity of the internal volumetric sensor, and we never had any trouble with it again.

Maybe you have a moth in there?

Mick.

[StellaArtois86]

Nope we’ve looked everywhere! I read about that on another forum so did a check. Doesn’t appear to be anything internal, removed everything that could possibly be a culprit!

[Chippy01]

Have you had the 12 volt Battery checked out? New batteries can sometimes carry internal faults.  Maybe a parasitic drain on the system somewhere?

A drop in a couple of volts of the Battery might cause the alarm to activate.

[Gerg]

I don't know the details of the alarm fitment in the car you have, but there is often a button (detailed in the car's owner's manual), sometimes fitted next to the front courtesy lights in the roof, or on the car's 'B' pillar, that if pressed just before the car is locked disables the interior alarm sensors until the next opening cycle.  This might help you diagnose what is triggering the alarm.

It is usual for there to be two alarm horns, one behind the radiator grille that is the one you hear from the horn push (that one is easily disconnected from outside of the car, so not used by the alarm), and another that will be fitted away from the front, less accessible, in the engine bay.  I am surprised they seem to have disconnected the wrong one.

Just for your information, If any electrical load (e.g. door light, dash cam?, boot light etc.) is placed on the Battery after the alarm is set, then the slight lowering of voltage that the Battery will suffer will be detected as 'activity' and the alarm will sound.  At least that's how it used to be!  If the 12v Battery is old/faulty, then as it slowly discharges over time (normally), it can have a sudden small voltage drop, which fools the alarm into thinking something has turned on. That is very rare problem though. 

[kithmo]

Does the alarm have its own horn even ?

SWMBO's Gen 2 had the same problem and disabling the interior motion sensor (like Gerg said) cured hers.

[Mick F]

19 minutes ago, kithmo said:

Does the alarm have its own horn even ?

It should have, though I don't know how Toyota does it.  Our Yaris has no alarm, thank goodness.  Pointless things IMO.

No point in using the normal horn as it can be seen and disabled by the would-be thief.  The best thing is for the alarm horn to be hidden and un-getatable.

Mick.

[Heidfirst]

if you lock the car with the mecahnical key it usually doesn't set the alarm on a Toyota.