Lexus GS Auxiliary Battery Alarm Issue

I had a similar issue with my GS. The car alarm started acting up, and I eventually traced it back to the auxiliary battery for the alarm system. These cars have a separate small battery just for the alarm. It's possible yours is discharged due to age. How old is it?

Thanks for the quick reply! That's helpful to know. I wasn't aware of the extra battery. I'm not sure how old it is, as I've only recently acquired the car. Where exactly is it located and is it difficult to access?

On my car, it's located in the trunk, near the main battery. You have to remove some trim panels to get to it. I'd suggest getting it checked out by a mechanic. A defective car alarm system can cause more problems than just an annoying alarm. They can properly diagnose the issue and tell you if it needs replacement. I've heard a defective alarm system can drain your main battery too.

Thanks so much for the advice! I took it to a local workshop, and they confirmed it was indeed the auxiliary battery discharged due to ageing, just as you suspected. They replaced it, and the alarm system is now working perfectly. The final repair cost was around 330€, including the system diagnosis.