Is200Se Alarm Going Off

[eigenvalue]

IS200SE, Year 2002

Just had two instances of the alarm going off for no apparent reason. Car was locked and sitting in the driveway at the time. Did change the main car Battery last week but there was an instance of the same thing a few months back before the Battery change. There is also a new Battery in the keyfob.

I have read the earlier forum threads on this problem, such as this one:

http://www.lexusownersclub.co.uk/forum/index.php?showtopic=72491&st=0&p=752743&hl=alarm&fromsearch=1entry752743

I intend to try locking, then turning off the motion sensor to isolate that as the possible problem. I also suffered from the 'headlights on' problem during the winter before last. No problem last winter which was at least as cold. No sign of moisture in the footwell fuse box but using a hairdryer and WD40 seemed to cure this problem.

Not sure what all the possible trigger sources for the alarm are - certainly the door, etc. switches and internal motion sensor in the roof light. Are there any other alarm sources? Also, are any diagnostics possible, e.g. with a code reader to find out the source of an alarm trigger? Is anyone able to provide any information or advice on this? Thanks to all.