Alarm In The Night

JBPRX400h · July 18, 2014

The night before last the alarm in my 2009 400h parked outside on the drive started going off after we had gone to bed. I turned it off using the remote on the key by unlocking then relocking from the bedroom window. There was nothing to see that was untoward.

About half an hour later the alarm went off again. I again cancelled it from the bedroom window by unlocking and relocking. I then got dressed and went out to investigate.

There was nothing apparent around the car so I unlocked it, opened the door and had a good look around inside. Again nothing apparent.

Got out, closed and locked the door and went back to bed.

Since then nothing.

Any ideas?

JBP

rayaans · July 18, 2014

Fly's, vibrations, anything that moves inside will basically set it off. Even if something fell, it will go off. As long as there is no damage to the car, its probably something inside.

However, if it keeps happening, it could be a loose wire. Had a loose wire in my dad's Merc about 10 years ago which kept repeatedly setting the alarm off

DanD · July 18, 2014

Yep, probably a moth or other wild life.

ColinBarber · July 18, 2014

did you just lock the door with the key to disable the alarm? Personally I would have just disabled the interior sensor rather than disabling the whole alarm - it is normally the motion sensor that causes false alarms, or some wildlife shut in the vehicle.

Either that or somebody setting it off hoping that you will disable it.

Chosen One · July 24, 2014

I had exactly the same problem a couple of years ago, the answer was A MOTH, as soon as I got him out problem solved.

bob999 · September 19, 2019

hi. I have a very similar problem. started 2 nights ago with my 2016 RX. random repeated alarm triggering. no sign of tampering. masked off the dashboard motion sensor last night but didnt solve the issue. did you find the root cause of your problem? Please help, I need a good nights sleep.

Herbie · September 19, 2019

1 hour ago, bob999 said:

masked off the dashboard motion sensor

I've not got a series 4 but are you sure it's in the dashboard?

I thought the light sensor was on the dash but alarm sensor is usually up in the courtesy light housing with a button to deactivate it.

Lydiamight · September 19, 2019

A fairly well known for car thieves to operate during the night is to rock the car so that the alarm goes off, run away and hide. Repeat enough times until the owner gets fed up with getting up and resetting the alarm and eventually turns off the alarm with a view to investigating in the morning.

Problem is that in the morning there will be no car to investigate

Chosen One · September 19, 2019

Thankfully we live in a crimefree area, although I can see what you mean. In addition to the standard Lexus alarm system I've fitted a tracker which is very well hidden, which has a feature in it that enables me to not only trace the whereabouts of the car, but I can disable the ignition from my mobile phone which turns off the engine etc. So even though a thief might take the car I don't know about it, I can do something about it.

Vince Donald · September 19, 2019

Crikey, this was an old thread resurrected.

I had something similar on my 2015 IS300h a few weeks back. Got home from work, parked and locked up, around 9.15pm, alarm goes off, so I reset it check everything, about half an hour later it goes off again, and then again about another 20 minutes. I disabled the interior sensor, never went off again. Next day I find an insect in the car, about 2cm long like a small cricket or grasshopper, something I see many of when cutting the lawns, so that was the culprit.

A couple of nights later it happened again, this time as I got in to disable the sensor I saw a moth flying inside, left it disabled, would have only got more in if I tried to get it out in the dark.

Next day was really hot, think it may have finished the moth off, never gone off since.

In over 30 years of driving, I've never had a car where an insect set off the alarm, these Lexus have damn sensitive alarms 😁

Vince

Barry14UK · September 19, 2019

Had my RX for nearly 11 months now and alarm went off once for no apparent reason with car on drive - no evidence of attempted tampering or insects also no traffic and windows were closed. No explanation and OK after reset - just hope it doesn't happen again! A similar thing happened with my BMW some years ago and dealership reckoned it must have been a spider, although I never found one. Bit of a pain for owner and neighbours when it happens.

PCM · September 20, 2019

Mine was triggered by the dash-cam falling down..

Arth_Vader · June 4, 2023

We’ve just had this with our 450h

Three nights in a row - 10pm 10pm and after midnight. Called Lexus after second one who asked us to check for insects and cobwebs so I dusted the car for cobwebs and sprayed it with fly spray to kill any insects.

Also turned off internal sensor, but you’ve got to remember to do that every time you switch off?

After night three alarm, after midnight (neighbours must be getting annoyed now) I went out and bought a steering wheel lock, so we could turn the alarm off (we can’t have the car taken away to Lexus for “reasons”)

Anyway - worked out what it was. A half full two litre bottle of water was on the front seat. At night it was cooling down and you know when the bottle cracks as the air inside contracts? Triggered the alarm.

Removed the bottle - nothing since.

RONNIE W HODGEKINSON · June 5, 2023

On 9/19/2019 at 11:56 PM, Barry14UK said:

Had my RX for nearly 11 months now and alarm went off once for no apparent reason with car on drive - no evidence of attempted tampering or insects also no traffic and windows were closed. No explanation and OK after reset - just hope it doesn't happen again! A similar thing happened with my BMW some years ago and dealership reckoned it must have been a spider, although I never found one. Bit of a pain for owner and neighbours when it happens.

It Was A Lucky spider Barry Good luck is coming your Way....................................................................................................

Las Palmas · June 5, 2023

On 7/18/2014 at 7:16 PM, ColinBarber said:

did you just lock the door with the key to disable the alarm? Personally I would have just disabled the interior sensor rather than disabling the whole alarm - it is normally the motion sensor that causes false alarms, or some wildlife shut in the vehicle.

Either that or somebody setting it off hoping that you will disable it.

If no doors are opened when alarm is turned off the car will automatically lock doors again. At least the one we have does so.

RONNIE W HODGEKINSON · June 5, 2023

On 7/18/2014 at 10:58 AM, JBPRX400h said:

The night before last the alarm in my 2009 400h parked outside on the drive started going off after we had gone to bed. I turned it off using the remote on the key by unlocking then relocking from the bedroom window. There was nothing to see that was untoward.

About half an hour later the alarm went off again. I again cancelled it from the bedroom window by unlocking and relocking. I then got dressed and went out to investigate.

There was nothing apparent around the car so I unlocked it, opened the door and had a good look around inside. Again nothing apparent.

Got out, closed and locked the door and went back to bed.

Since then nothing.

Any ideas?

JBP

Its Been A Crawley ( No Not one Of the Actors From Downton Abbey But A CREEPY Crawley With Six Legs Barry

Barry14UK · June 6, 2023

Ha ha. Can laugh at it now but most annoying at the time and undoubtedly for neighbours too. I did thoroughly clean the interior and spray liberally with insect killer. Took a couple of days to clear smell but worth it!

ColinBarber · June 6, 2023

On 6/5/2023 at 7:56 AM, Las Palmas said:

If no doors are opened when alarm is turned off the car will automatically lock doors again. At least the one we have does so.

Yes that's correct, if the doors aren't opened within 30 seconds they re-lock by default. But the OP stated they opened the door then locked it.

Phil G · October 4

The alarm on my 2017 RX450h goes off in the middle on the night approximately once a week even with the internal sensor switched off. The dealership say this could be because of the 12v Battery being old and having a low voltage (colder at night therefore Battery voltage reduces).

Is this an issues and would a new Battery need to be registered with the on-board computer system?

ColinBarber · October 4

20 minutes ago, Phil G said:

Is this an issues and would a new battery need to be registered with the on-board computer system?

It is possibly the cause (if you have a multimeter you could measure the voltage in the morning before you start the car to confirm). If you change the Battery, you don't need to register it - just reinitialise the window auto open/close by following the procedure in the owners manual.