After my brother left the interior dom light and drain the battery, the alarm been acting up lately. Most of the time now when I take out the key before arming the alarm system, the system goes off for no reason. I like to know why it doing this and if there was a why I can reset it some how or fix it.

thanks

Most likely your battery needs replacing, especially if it is the OEM battery. A deep discharge cycle such as you've experienced is often the straw that broke the camel's back. While the battery will still start the engine and operate the lights, a damaged cell with high internal resistance can often throw the available voltage - with the engine off - out of range for normal operation of the more sophisticated electronics available on today's cars. Setting the alarm involves engaging all five lock solenoids simultaneously - a brief but significant load - that may pull the voltage below minimums for the alarm.

Frustrating? Sure, but at least the fix is (relatively) cheap. If possible, have a local retail store like Autozone check your battery under load. It's free, and may save you a lot of head scratching. Good luck!

thanks Lil4x.

that very helpful.

bored7one4,
Was your problem fixed? My girlfriend just picked up a 2000 RX300. The battery died and she had it replaced. Since then, the alarm will arm and go off by itself about 15 -25 seconds after turning off the ignition. Also, if the doors are unlocked and closed, they will automatically lock after 30 seconds or so.

I've tried unconnecting and reconnecting the battery, but didn't help. Anyone have any suggestions?

Thanks in advance for the help!