Not sure, of the correct name for these little units one each side of the windscreen. I am assuming they are security sensors to stop stray hands reaching inside the vehicle when the top is down. Trouble is the ones I have don’t seem to do anything, the passenger one has an LED, which illuminates when a hand is waved in front of it, the driver’s side has nothing. No alarm sounds when the car is locked and my hand is waved inside even when the LED is lit. Any ideas please how these should work.
They certainly look like PIR motion sensors which would be part of an aftermarket alarm system.
If you have the installation guide it may tell you how to activate them.
I managed to find a downloadable user manual and installation guide on the internet for my aftermarket alarm system.
HI
They're actually ultrasonic doppler sensors (1 transmit, 1 receive).
I have them in my car! They're part of the Mercedes OEM Alarm system.
They're working exactly as intended, from your description. They are however disabled when the top is down. (they won't work reliably in open air!).
With the hood up, or hardtop on, the alarm should sound when triggered by these units. (shown by the LED coming on!)
HI
They're actually ultrasonic doppler sensors (1 transmit, 1 receive).
I have them in my car! They're part of the Mercedes OEM Alarm system.
They're working exactly as intended, from your description. They are however disabled when the top is down. (they won't work reliably in open air!).
With the hood up, or hardtop on, the alarm should sound when triggered by these units. (shown by the LED coming on!)
just my 2 cents worth!
IAN
Thanks for that explanation Ian, perhaps they were only fitted to later models or were an option because I can't find them on my car.
My Toad alarm must have something similar because if walk near the car with the alarm set, it lets out a series of audible bleeps.
HI
They're actually ultrasonic doppler sensors (1 transmit, 1 receive).
I have them in my car! They're part of the Mercedes OEM Alarm system.
They're working exactly as intended, from your description. They are however disabled when the top is down. (they won't work reliably in open air!).
With the hood up, or hardtop on, the alarm should sound when triggered by these units. (shown by the LED coming on!)
just my 2 cents worth!
IAN
Hi Ian and thanks for your reply, I have tried sitting in the car with the roof up and windows closed with the alarm on. Although a red LED lights up when i wave my hand in front of the sensor, that's it no alarm sound or anything. Is there a way that they may have been switched of and if so how do you switch them back again.
Hi Malcolm,
Yes, you can disable the interior sensors by holding a "black touch key" against a stud in the glove box. The Mercedes alarm booklet talks about a "black touch key" and a "red touch key"... I have neither of these items for my car! (Also my mating stud / titty thing is actually in the carpeted closure panel above the driver's knees, covering the steering column.. not in the "glove box")
I've taken the liberty of scanning the alarm user manual, and am attaching it to this message (hopefully!) for anyone who wants to read the "oracle" on this alarm. I believe this alarm is dealer fitted, and possibly only applicable to the UK market.
P.S. Just had to chop the back page off the manual, in order to get it within the forum size limit! Enjoy!
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