Alarm goes off by its self, dome light comes on by its self

Focusing on switches: Start with the door switches. Pull the fuse for the dome lights. Reset the alarm. Does it sound off? The alarm feeds off the dome light fuse. Driver door is first: Often they wear out first and give us grief like this. Unscrew and disconnect the switch first. Replace the fuse. Carefully close the door so you don't loose the wire in the frame(attach a string to it so you can fish it back out if it falls in). Reset the alarm. Does it sound off or not? If it does, it is other than the switch or the passenger door switch (if a 2 door or 2 other passenger switches if a 4 door). Repeat process until the switch is found or all are eliminated. Switches are cheap, so replacing them will not break the bank. Disconnect the fuse again, unscrew the bad switch. Unplug it. Plug in the new. Screw it back in place. Reconnect the fuse and try it again. Repeat as needed until you have either found it or just limited your search area. Most often you will stumble upon it- chaffed wires, look plugs, bad switches). Yes, there is more, but I see this as the usual suspect. If you go back into the alarm, disconnect the alarm first, then observe the dome lights with the fuse in. It just may be a faulty control in the alarm, which is out of my territory. Let us know what you find, but start with the smallest things first. Good Luck!

clean and lub your door closing mech.

Lock the car and then pull each door to see which one is setting the alarm. Once you know which door it is, find the switch in the door jam that operates the dome light. If the switch is adjustable, adjust it out a bit until pulling on the door no longer lights the dome light or sets off the alarm. If it's not adjustable, perhaps you need more body work to fix it. Another option is to disable the switch by removing it, disconnecting the wire, taping the wire, and letting it go inside the body.

When this happened to mine it ended up being a bad door switch. The alarm, dome/map lights and electric door locks are all connected to the door switches. It cost $65 for diagnosis, parts and labor at Saturn of South Burlington VT

To temporarily solve the light problem, I taped a washer to the inside of the door where the door hits the plunger on the light switch. A permanent solution would be to drill a hole in the door at this spot and put a self taping screw in that will trigger the switch sooner. I figured out the reason the dome light stayed on is due to the courtesy light timer and the lights would have eventually gone off.

Check your door switch, open the door and see if the dome light comes on in the car.If it does then your problem is with the alarm wiring going to the door switch if it doesn't come on then check your fuses.

do you have a factory alarm does it set and after you set it can you still open the door with out the alarm going off. roll window down and try that if that is the case door latch could be bad or wires going to door latch bad.

USUALLY POWER WINDOW PROBLEMS ARE ONE OF THREE THINGS. 1. SWITCH 2. MOTOR 3. WINDOW REGULATOR. THE MOST COMMON PROBLEM THE LEXUS HAS IS THE MASTER SWITCH IN THE DRIVERS DOOR. IT CAN ALSO AFFECT THE OPERATION OF THE PASSENGER DOOR SWITCH....IF WINDOW REGULATOR IS BAD YOU WILL HEAR SOME CRAZY NOISES COMING OUT OF DOOR PANEL...VERY OBVIOUS.... FOLLOW THIS CLOSELY...STARE AT A LITE DOME LIGHT USUALLY WITH DOOR OPEN...WHEN YOU PRESS WINDOW SWITCH, IF THERE IS ANY DIMING OF DOME LIGHT....MOTOR IS BAD. IF DOME LIGHT STAYS THE SAME BRIGHTNESS... SWITCH IS BAD... EXCEPT IN THE CASE SOME HACKER HAS BEEN IN THE DOOR PANEL BEFORE ...IT DOES TAKE A SPECIAL TALENT TO REMOVE DOOR PANELS WITHOUT BREAKING THINGS AND EVEN MORE TALENT TO REPLACE WINDOW REGULATORS

if you hold the key in the trunk or drivers door, to the unlocked position for a few seconds the doors will unlock and the windows will all go down. usually when this happens by its self the body controll module is to blame. it could be the electrics on the drivers door lock broke in the unlock possition. the door handel/lock is a nightmare to replace. i would get a used body controll module and plug it in and try that first

This is caused by the door jamb switch.  This is the sensor that, if the door is open, the dome light goes on and the alarm beeps if keys are in the ignition, or even the headlights are on.  Sometimes they just fall apart b/c they are plastic.  It costs only a few bucks.  Pull it out with pliers and and plug in the new on.  Takes 1-2 minutes to do.  Just make sure you do not lose the wire harness in the door when you pull out the junk one.  You can also break, crack, or do whatever to the old one.
One way to test this is to open one door at a time, and if you do not here the alarm buzz when the door is open, that is the one that is busted.  Good luck