So I just got my W126 last night.

I know Im supposed to post a car picture first. It was dark and then I started taking tings apart.

I could not wait to dig into the battery box area behind the bulkhead. I had to see if the CA car had any hidden rust.

Thankfully it was rust free down there (other than the tray itself)

But while I was in there I found this odd sensor. (the one in my hand)

IMG_0068 by ttownthomas, on Flickr

It says muRata on it. It looked like it was hot glued on to something at some point and there is no MB part number. <-makes me think it is not a factory part

I found this site: https://www.murata.com/en-us and the logo matches.

Could it be part of an aftermarket alarm? My best guess is some sort of buzzer

Is it safe to say, with the lack of replies, that this is not a MB part?

Looks like a piercing speaker to discourage further malfeasance in its proximity. Probably part of an aftermarket security system. Where do the wires lead?

I’m pretty sure it’s not a MB part. It doesn’t show in W126 wiring diagrams.

Sixto
98 E320s sedan and wagon

MuRata makes electronic parts ( mostly capacitors ) . Looks like a piezo alarm, and probably not that loud a few feet away.

Its a sonic sensor --a part of your alarm system /

I'll have to trace the wires. The red wire was broken and I don't have the alarm key fob that is described in the owners manual for the aftermarket alarm. I'll be removing whatever is leftover