A171 820 25 26 and the replacement A 219 820 32 26 are both getting old. New ones are unobtainable and used examples expensive, considering that when you take them apart to replace the batteries you're likely to find them fried. A2048705726 is more modern and there's a plentiful (cheap) supply of used ones. Casing isn't quite the same and the connector different (although still 3 terminals). Does anyone know if it has the same PCB?

 

Curious myself. Following.

 

Who cares? MANY of us have had the old "my battery keeps dying so I disconnected the siren and now things are OK" - this has become so common, that at local tech days, one of the things we do is disconnect the siren for those who are timid about tearing into the car, as a service to fellow owners. This way, that particular owner never has to deal with the siren doing what they all do as they age: Drain the battery.

ANY used siren you buy, if the batteries are not already leaking, soon will have leaking batteries. If you can find one that is in good shape, you MUST replace the batteries before putting it in the car - again, 20 year old batteries are a ticking time bomb.

Way easier to just disconnect the damn thing.

 

Here are two sirens that beep, 219 820 32 26 this has a 8 mm stud on it, so you’ll have to find a nut. The other is 171 820 53 26, this one uses a 8 mm screw like the Crossfire.
It is mentioned that they could be getting too old, no worries there as they have the manufacturing date printed on them.

 

Bob McCubbin on Fakebook says this is the only one he can find in stock:

https://www.mboemparts.com/v-2003-me...EZX3AgW6dz9JeA

 

There must be more around Mercedes must have used these in plenty of models so I doubt they would let the supply dry up.
Try changing the first two numbers of the four two numbers they are the modification numbers.