There is a lot of expertise here. Thought I would toss this one out and see if anyone knows.

The alarm siren on my 2000 540iT failed (well it still worked but was about as loud as a mouse). Replaced it but the replacement does not work properly (told the dealer they gave me a bad one and a 2nd unit acts the same way).

Everything works the way it should EXCEPT when the alarm acutally is triggered. Instead of getting the hi-low-hi-low alternating tone (as it use to do), it just gives a continious ear pearcing hi tone. I would expect the alternating tones are gererated in the siren unit, but apparently not.

Any ideas? Is the alarm module damaged?

WHen I took apart the old siren (difficult, it's not meant to come apart) there is a fair amount of circuitry and something was definately blown on it (blackened area and really stunk) :confused

Mine sounds more like a house alarm - a series of many high pitched notes going up and down and up and down. It's very loud, but there are many more notes than just one or two there.

Mine sounds more like a house alarm - a series of many high pitched notes going up and down and up and down. It's very loud, but there are many more notes than just one or two there.
Yes that is how it sounded before the siren was replaced. I'm guessing when the original siren below, it damaged the control unit (although I would think the varying tones would be generated in the siren module)