Alarm System Comes On Randomly, 2006 Prius

[Flymark]

The Theft Deterrent alarm began triggering randomly... up to five times an hour with the vehicle sitting locked in the garage. After several dead-end troubleshooting paths on PriusChat and with Toyota dealer, I discovered moisture in the Battery compartment of the Smart Key fob. Dried out fob, replaced Battery and problem went away... for about three hours, then resumed. Opened Battery compartment in fob and found new moisture. Removed battery a second time, set key fob aside to dry thoroughly and started using backup key fob. No more alarms! Seem to remember dropping key fob into slush some time ago.

[IanIanIanIan]

I had problems in my Gen2 with wireframe sunglasses being stored in the overhead, then later with a small fly trapped in the cabin.

Annoying is it not when the answer is not obvious.

[Grumpy Cabbie]

I'd check your 12v and if it's the original 12v then I'm 95% sure that will be the cause.

The 12v in a Prius or Toyota hybrid isn't as 'strong' as in a traditional car as it doesn't need to crank the engine. All it has to do is fire up the main computer which then fires the engine via the large HV Battery. Because of this you are unlkely to know the 12v is failing as it either works or then suddenly doesn't. A traditional car would turn the engine over slower and slower for a week or so before hand.

When the Prius 12v does start to fail (like when it's 8 years old in cold weather) it throws up all sorts or weird, wonderful and alarming error messages, the central locking plays up and the alarm goes crazy.

It might not be your 12v, but your car is of the age they start to go (usually 5 years or 80k miles) and it's a cheap and easy fix.

The other thing it 'might' be is whether 4g has come to your very near area. Me and my Toyota owning neighbours all had alarm and locking issues one day and it turned out O2 had also updated their nearby mast to 4g. The 800 mhz (actual varies 760-860 mhz) was interferring with the 433 mhz remotes on Toyota cars. My Prius, the Mrs's IQ and a neighbour with a Rav4 all had the issues brought on suddenly. O2 totally denied it but sent an engineer early the next day. Within minutes of him arriving the issues resolved. Apparently coincidence.

Let us all know how you get on.