rain triggering the alarm

If this hasn't been caused by rain dripping in and setting off the intrusion sensor, then (and I'm only taking from experience with my S1) it could be one of the little button contacts for the doors that's gone a bit duff. The sensor for my boot lid became rather dodgy and the alarm would trigger on it's own. I had it replaced at service time and it's been fine for years since.

Perhaps corrosion and the added moisture in the air is tripping one of yours?

The alarm tell tale (flashing red light on dash) flashes in different sequences to indicate the cause of an alarm.

From my S1 manual for Cobra 6422 alarm...

- Single Flash followed by 2 second break: Caused by door, engine lid or front bonnet sensor. A sensing switch may require attention.
- Three flashes followed by 2 second break: caused by the intrusion sensor. If there are no loose or moving objects or animals (check for mice?) in the vehicle, the sensitivity of the sensor may need adjustment by your dealer (isn't it always the case).
- Four flashes followed by a 2 second break: Caused by the ignition circuit being energised.

Hope that might be of some help.

The false alarming in rain is probably caused by rain water dripping down the rear bulkhead and causing the microwave sensor to trigger the alarm.
The microwave sensor is mounted indide the car on the rear bulkhead between the seats.
You will need to remove the seatsand rear plastic trim to access it.

The sensor has a adjustment screw on it. You could try and turn the sensivity right down and see if it still false alarms.

If it stops the false alarming, one fix is to remove the sensor and mount it back on with a large square of thick foil between the sensor and the bunkhead.
This will stop the sensor seeing the waterv movement in the engine bay.

With all due respect, before you start to dismantle your car to see if you have an over active interior sensor, please check the alarm codes to see where the issue actually is. If it is an interior sensor sensitivity issue, then the thread link at the bottom discusses adjustment in more detail. However, I'd imagine that if water is leaking into the car and setting off the alarm, then the solution would be to identify and stop the water ingress rather than adjusting the alarm. The LotusTalk thread seems to go as far as to say that a harsh environment (like very heavy rain) is likely to set the alarm off (it doesn't say why though) and that the solution is to just disable the interior sensor for the duration (the doors and ignition circuit are still protected). If you aren't getting persistent problems, then taking tools to your Elise might be a bit extreme.

From the manual for the Cobra 8185/8186 Alarm System (which I assume your 2007 model will have):

Note: If the alarm has been triggered in
your absence a 'status history' will be
displayed by the LED warning light and is
indicated as follows:-
>> Single pulse flashing of LED: One
alarm state caused by opening of the
boot, bonnet or doors.
>> Twin pulse flashing of LED: One
alarm state triggered by optional
microwave sensor.
>> Triple pulse flashing of LED: Alarm
state triggered by the ultrasonic
sensor or optional glass break.
>> Quadruple flash repeated regularly:
Alarm state caused by an attempt to
start the car.

And also from here:
http://www.lotustalk.com/forums/f320/guide-alarm-i...

Symptom; Interior Microwave sensor triggers alarm.
Probable Cause;
a) Environment too harsh (heavy rain, thunder etc).
b) Sensitivity
Solution;
a) Temporarily bypass Microwave by arming the alarm normally and then pressing the smaller “B” button twice within 20 seconds.
b) Adjust sensitivity of Microwave by either removing interior rear bulkhead panel, or drill hole in panel to gain access to adjustment.

(Microwave adjustment thread here: http://www.lotustalk.com/forums/f320/enabling-micr... )

I found the alarm on my 111R went off if I washed it with the alarm set. I reckoned the trigger was water running down the rear window, but I never proved it. Just a thought...

I've also had this issue for the past 3yrs,every time it rains hard since I've owned my 111r. The alarm even goes off when its underneath a car cover,which is waterproof and tight fitting.
I've got used to the late night wake up calls to tell me its raining and kept the spare keys close to hand.
I was advised to turn the sensitivity down on the motion sensor & adjust the switches on the body panels as it doesn't take much to set the alarm off by just touching it but I quite like the sensitivity and will hopefully act as a deterrent!