Alarm goes off randomly
 

Looking for some advice on what to do next and maybe what to tell the dealer to look for. The factory alarm on my wife's 2012 RX450h AWD has started going off 2-3 times per night usually between midnight and 7am (it happened once on a saturday around 11am, but otherwise its always at night). It's not every night, but it is frequent...roughly 2-3 nights per week. I have to park it on the street, no garage or driveway in my area. Every time it happens, I look out the window or go outside and there is no one around, no cars just drove by, no cats, raccoons, etc. near the car. Happened once about 5 weeks ago, then it was fine for 3 weeks and started in again, but more frequently recently.

I bought it about 2 &1/2 months ago from a Lexus dealership in a different state...It was a dealer loaner previously. I have 2 key fobs....one for me and one for my wife (she is the primary driver). So far (as far as we know) the alarm has only randomly gone off like this while we are both at home (night time)...this made me guess that maybe it was a key fob problem, so I put a new battery in each key...that did not fix it.

A coworker said that maybe the dealership could adjust the sensitivity of the sensors (he was thinking maybe just wind or something was setting it off)....I took it in today and they said there was no way to do that on this vehicle and that they inspected the alarm and it seemed like everything was okay to them. I felt like I was kind of just blown off. When I reiterated to them again how frequently it happened and they agreed to keep it and look at it again tomorrow. I asked if they could just turn the alarm off (not ideal, but if it got me a full nights sleep I'd rather them do that then nothing) and they acted like that wasn't possible, but I never got a really clear answer from them.

I have pretty low confidence level that the dealership will be able to do much. Assuming that whatever the dealer does next does not fix this problem, any advice on what to try next? I was thinking that maybe one of the key fobs is just defective since it only happens when both key fobs are at home...so maybe I should just take the battery out of one and my wife and I can share a single key except in rare cases I could just pop a battery in the extra if needed. Coud a bad key fob even potentially be the problem?

Another thing I have read is that a low car battery could cause the alarm to malfunction. I can't imagine it needs a new battery with only 15,000 miles on the car, but I was thinking that for $100 or so that it might be worth just replacing it in hopes that was the problem.

Any other ideas, advice, or thoughts on what to try next?

some sort of radio interference is my guess. I cannot park my cars locked in my garage because of the same problem so I leave them unlocked. I have yet to find out what is causing it as it happens to two brands of my cars

Interesting discussion. For my edification, other than opening the doors or hood while the car is locked what else would "normally" set off the alarm? Other than the door position switches in the door jambs and engine compartment, what else is there? (Glass breakage is an option) When someone tells you to adjust the sensitivity of the sensors, what sensors?

I've seen some discussions that the door position switches are not working. JBX have you noticed your interior lights on when the doors appear to be closed? If you have a failing door switch, you'd see that happen. Not sure you would see anything unusual if the hood switch was failing. You'd get a message the hood is open when starting the car. With bad door switches you'd probably get random dinging when the car is unlocked or it won't lock as it sees a door open.

RXSF, does your problem occur day or night? Does it occur immediately adjacent to, but not in the garage? What's powered up in the garage? Refrigerator/freezer/furnace? Probably not a furnace in SanFran.

DunWkg: I have not seen any interior lights on at all when I expected the doors to be locked, but that is a good thought...I'll keep an eye on that for sure. I haven't received any hood open errors either.

Have had a similar experience with our 2010 RX450h, although so far only 3 instances each at about 11pm. I'm calling the dealer in Brisbane, Australia tomorrow

Do you have the 'glass break' option on your RX? If you do, there is a sensitivity adjustment for that. Just a thought.

I have only had my 2011 for 3 weeks. It happened to me one time. I believe it is related to the door sensor on my driver's side. Basically the door sensor doesn't retract all the way when you open the door, you will notice you have the door light, but the interior or dash light won't come on showing you open the door. You can actually test the switch by pulling it in and out manually

No clue...since I bought it used...is there an easy way to tell -- other than breaking the glass to see :) ?

Thanks...I'll test this out when I get the RX back and see if I see the interior or dash lights doing something unexpected with regard to the doors.

Had the same problem on my 2010 RX hybrid. It only occurred while on vacation and parked outside in Florida. I thought it was heat related but after reading this, I guess not. It never occurred while in Kentucky or parked in the garage. Hasn't happened in over a year. Weird.

It only occurs when I park in the garage (single space). I have a refrigerator in there, washer, dryer, and also my home alarm system which I suspect is the cause of all this.

I have had my old RX alarm go off in the middle of the night without me knowing and by morning the battery was dead.

It doesnt matter night or day, just whenever I have it locked and parked for a few hours

Alarm randomly goes off FREQUENTLY 2010 RX350
 

HELP ... Alarm goes off randomly... here's what I've done so far. (First-timer... Sorry for the long write-up... but I do try to be clear and complete!)

Bought 2010 RX350 used two years ago, no problems at all until having hood recently repainted. Not sure the two are related... but shortly after (two days) had one-time warning of "hood loose" on dash while driving (pulled over to check... it was tightly secured). No repeat on the hood warning since.

Days later, the alarm went off on its own early in the morning, turned off with remote from house. Dew coated the entire car and inspection shows no-one tried to get in. (No smudged in dew) Alarm sounded again minutes later, I was actually outside, ~30 feet away, so I verified no-one was near. Reset with alarm and it stayed quiet.

Replaced batteries in both fobs. Pulled battery (unknown age, no sticker and was in car when purchased.) and had checked by Autozone... 'good battery'.

Alarm went off again that night. Reset with key fob and pulled battery contact for night time quiet.

Next morning I visually inspected under hood area (after removing all the plastic parts) and saw nothing obviously wrong. Clear of dirt and debris, no crushed wire bundles etc. WD40 to the hood latch and switch area best I could while still installed. Reinstalled battery and hoped for the best.

No alarm that night (yeah!)... however, alarm again went off 2 of the 3 following nights. Again pulled battery contact so we/neighbors could sleep.

So it's gone off only at night, in cool weather and warm, moist and dry (I doubt it's weather related.)

I found many references to faulty hood latches in forum/internet searches. That coupled with the only thing done to the vehicle recently was in the hood area prompted me to pull the hood latch, inspect the attached switch and ultimately disconnect the hood latch switch in order to isolate it from the system.

Performed many pre and post- alarm system checks with similar results after disconnecting the hood latch switch. Shock the car, pulled locked door handles etc. but never could get the alarm to sound, even with the door closed/locked, window open and fob 30 feet away. Reach in thru open window to open door yields no alarm. So I have never been able to set off the alarm.

Only differences between having the hood latch switch connected and not were these... the 'hood loose' warning is not evident with the switch disconnected and .... the alarm light on the dash. With switch connected, when the car is turned off, doors closed and locked, the dash alarm light blinks immediately and stays so. With the hood latch switch disconnected, and the doors closed/locked, the dash alarm light is solid for the required ~30 seconds and then the light changes to blinking.

I really thought/hoped the switch was at fault, perhaps fouled by paint work or knocked out of adjustment.

However, with the hood latch switch disconnected I still had the alarm randomly go off again that night. Battery disconnected... and now I'm here begging for insights from anyone who has dealt with this issue.

Can I turn off the alarm system? Are there other/better ways to test it? I REALLY prefer to avoid the dealership... not known for integrity or helpfulness.

Can anyone shed some light on this? Either your (hopefully successful) experiences with like occurrences, or knowledge from those more familiar than I.

I appreciate any feedback! Thanks... Cliff

BTW, Battery reads 12.36 vdc at terminals while connected to car. Clean terminals, doors closed and locked.

I think your car battery maybe low and needs replacing.

Does the battery have any warranty left? Go to AutoZone and ask them to load test it. If it fails, then they can possibly look and see if any warranty left on the battery? If no more warranty left, you need to decide where you want to buy your next battery at.

Good luck.

Addendum: I really doubt the following, but it's possible. The following is more likely to happen to maybe an LX570 due to the great global demand overseas for the LX570. DO YOU see anyone around sitting in a vehicle (vehicles around you that you don't recognize) just looking at you. The reason I ask is there is a chance these bad folks are trying to intercept your key fob's signal and make a duplicate key fob. This has to be pretty close range (certainly not like quarter mile down the street watching with a pair of binoculars. More like just a few car lengths away type of thing.).