Alarm misbehaving...

[Idol hands71]

Hi everyone.
So.... just got a R171 for the wife, had it a week and all appeared well until last night.
when we were treated to Lights flashing and general weird electronic behaviour, including hazards and occasional alarm siren.
After disarming /opening with key fob after 15 seceonds or less it all started again...on trying to start up, just a click instead of turning over ... On investigation (at 1am...) i discovered the entire battery compartment full of water, (up to the top of battery). the drain hole was jammed with debris. The drain was cleared and all water now dispersed.
This morning after jump starting I realised the battery was flat, so 1 x new battery latter all appeared well, no problems all day, and as soon as things went dark and the temperature has dropped to zero or lower the hazards are going off, after pressing the open button all is well for a few seconds then off we go again... sometimes accompanied by the siren, sometimes just the disco lights.
I've read the blocked drain is commonplace, therefore I. Hoping people have also experienced this problem too.
Has water ingress the alarm system too? There appears to be a siren in the compartment, is this the one people (mostly American forums seem to disconnect)? Is it a costly replacement??
So before I head off to the local garage... WD40??? Short term solution or waste of time? Or is it a replacement???

Help, as the neighbours seem to be losing patience...!

 

[sonic]

My wife had two 171's & now has a SLC250d. Our cars are both garaged so they pick up very little tree droppings, but I always make a point of cleaning away all the bits in the area forward of the screen. I have had a small amount of water in the battery tray, that was a blockage in the drain. There are two other drains either side of the screen.
As for your fault getting the codes read is really the first place to go to, otherwise it could be expensive guesswork. MB's do not like low voltage & this could have triggered your faults.
I think if you lock the car manually with the key it does not set the alarm, could be a stop gap for the neighbours? In the menu drive I think there is a setting to turn off the internal acoustic sensor. Worth trying.

 

[mioba]

I would be getting into the flooded area disconnecting all visible wiring and getting everything thoroughly dry by parking with bonnet open and facing the sun and / or with the help of a hairdryer. Once things are dry and only then consider using wd40 before putting things back together.

did water get into fuse box - check.

The alarm is usually controlled in part by a module under front wheel arch. The batteries in them fail and they are prone to suffer water ingress.

 

[Abb]

The batteries in your alarm siren will more than likely be defunct! They are a sealed unit and over time the batteries deteriorate and leak all over the PCB they are attached to, giving all the symptoms you describe. You can of course just unplug it at the siren to stop giving you the headache it is currently presenting. A new siren is circa £100 from the dealership and is plug and play. Hardest part is trying to figure out where you siren is hiding! Normally under one of the front wheels arch liners.

 

[Idol hands71]

The problem only started after the battery compartment flooded, whatever the piece of kit is in there was under water and the problem started immediately after. When I lock with the key there isn't a problem, however one press of the fob and its like John Travolta's back bedroom.
What is the component inside the battery compartment??