alarm siren failure?? Car wouldn't start!!

Discovery 300tdi 1996
This morning my car wouldn't start,it turned out the 10 amp fuse (no 5 in satellite 1) had blown for Anti theft alarm.....

AA man (I'd tried everything to get it going) finally found this fuse had blown.....he didn't have a 10amp in his box so put on a 25amp. Car started straight away but immediately the alarm siren started to fry!! Smoke pouring from it!! Obviously switched straight off!!

My question is, would the fault definitely have been at the siren? Does anyone know if this fuse is for the feed just to the siren?
After the connections on the sirens has gone a bit melty, AA man said that they were probably causing the fuse to blow?
Do these sirens fail eventually? I know there is a battery in them so do these eventually pack up? This one is original from 1996.

......not sure I'm able to help you with the fuse issue but the batteries in the sirens do fail and no longer hold charge....mine has failed thank goodness so I was able to turn the damn thing off when I had alarm issues...however I didn't have fuse issues. I suppose a battery fault could lead to a short circuit

There appears to be a fault with the siren, unplug it and then replace the fuse to see if your engine will start.

The siren battery won't last for ever, mine has been been flat for around 10 years now.

That's cool, new fuse has done the job (10amp this time not 25amp) Will look for another siren at some point

What are to 4 pin plugs called that plug into these? mine is chewed up now.

Otherwise special day today...car passed MOT!!

The plug is not a LR replacable part as it part of the wiring loom, you my find s similar one on the auto wiring suppliers sites such as this. Auto Electrical Components, Parts and Accessories for Trade and DIY: Polevolt Ltd