Would swapping just the siren offer a solution? So the internals all match the car?
possibly. I've never opened one up, you'd have to see.... Probably just a speaker anyway
I think there's also a back-up battery in there, probably a good idea to check that as well ...
edit: specs for the siren module, according to elearn :
The main specifications of the siren are:
green batteries for self-supply if the cables are cut
battery recharging from command
programmable acoustic emission
serial dialogue with body computer and other alarm system components
The anti-theft device has a stand-alone siren which gives an acoustic signal to indicate an attempted break-in, on a command from the BCN.
The stand-alone siren is connected to the rest of the system with:
a dedicated serial line between NBC and siren
a supply for the siren/internal battery recharging
The siren can respond to the diagnostic messages sent by the BCN (internal self-test)
The siren is located in the front left wheelarch.
SIREN PIN OUT
1 - Siren supply
2 - Serial line
3 - Earth
4 - N.C.
Management of heart-beat command
During surveillance, the BC periodically sends a command to the siren, in order to check the condition of the serial connection between the two devices: this periodical command is called 'heart-beat' and allows any attempts at intrusion or cable cutting to be detected on the serial line.
Every 500 ms, the BC sends the heart-beat command via a crypto-rolling code to the siren and checks that it has been received correctly.
If the BC does not manage to send the heart-beat command, the crypto-rolling code is updated as follows:
the BC does not manage to send the command (e.g. because of a short-circuit on the serial line): the BC makes 2 further attempts to send the command without changing the crypto-rolling code.
the BC sends the command but the serial line is disturbed: the BC makes 2 further attempts to send the command without changing the crypto-rolling code.
the BC sends the command but the state of the siren is not correct or there is a loss of synchronisation on the heart-beat signal: the BC makes 2 further attempts to send the command, changing the crypto-rolling code at each attempt.
If after the attempts to repeat the command, the heart-beat synchronisation is not restored correctly, the BC changes to the alarm state and implements the necessary counter-measures (activation of blinkers, etc.).
As the siren also no longer receives the heart-beat command, the blinkers visual indication will be accompanied by the acoustic indication activated by the siren, which will intervene at the same time as the BC (for 3 failed attempts at heart-beat exchange made every 500 ms).
At all events, the heart-beat command continues to be issued until the system is switched off, and also during the alarm state.