Alarm keeps going off
 

Hello,

My lexus gs300 stock alarm keeps going off after locking with remote after few minutes.
Changed battery, and left it for ecu to reset around 20mins, still same,
When I lock doors with key, everything is fine then.
Any thoughts how to reset alarm maybe or what it could be wrong?

Thanks!

tried to unplug hood sensor and still same issue whan lock with remote it starts beeping after minute

i had this happen to me a few times.. once i drive around the block it stops doing this..safe to say my whole neighborhood hates me :(

Alarm
 

Something is opening after you set your alarm. I think your trunk might be moving up . Check your trunk how its closing .

I'm willing to bet that its a door sensor. When you close it, it says "door is closed" to the ecu.. Then after a bit it malfunctions and 'opens' sending the signal to the keyless entry to sound the horn...

But i was looking at night time if doors "opens" illumination should go on but it does not.
Maybe it could be related to trunk? Trunk opens up remotely and from inside, but recently for not using lock I am not able to spin key in trunk lock?

Same issue with a inconvenient remedy
 

I have a 1998 one owner es300. For the past 10 years, the car alarm goes off on its own. Nothing bumps the car or shakes it to make it go off. Sometimes it's in the middle of the day and worse at night. It was quite annoying to wake up to the alarm going off in the basement garage. no intruders or anything falling on it. Just completely random. To my knowledge there is no way to arm or disarm the alarm on the car. Even if I left the doors unlocked while running into a store or parked in my yard, sometimes just by opening the door, it would set off the alarm. I've changed out fuses and car batteries but it never fixed the issue. Sometimes months would go by without the hiccup but then there it was again reminding me something was up. So I every time I parked the car, I would lift the hood and remove the fuse for the horn, so when it would go off at least it wasn't disturbing the peace, but then it would drain my battery.
So, a year ago I installed a battery disconnect switch. Now every time I park the car, I lift the hood, unlatch the battery disconnect switch and close the hood. No more battery drain and no more alarm going off, and no way for someone to steal the car or forget that I took out the horn fuse. It's inconvenient, but it works. I just have to use the key to manually unlock the doors and pop the hood to connect the battery in order to start the car.
That's the only remedy I was able to find, due to Lexus being stumped over the issue. Super lame that this happens. I am curious to know what any of you have done to truly fix this issue?

Issue most likely is door sensors
 

So the door sensors are not the problem them selfs but the screw that used to hold them to the body of the car also works as a ground and for what ever reason, that screw loses contact with the body of car thus triggering either the Interior alarm when the car is running or the horns and lights when the car is turned off and parked. The solution is to unscrew the the screw from the offending door sensor look for rust if no rust I would just reseat the sensor &screw it back in.

if that does not work I would replace the door shut sensor.

Sounds like an issue with a door lock actuator. They have a switch built in that tells whether or not the door is LOCKED (not if it's open). If the actuator indicates that a door is UNLOCKED when the alarm system doesn't expect it to be, the alarm goes off.