Just got a Viper alarm installed, with the proximity sensor (DEI 508D).

I am trying to fine-tune the sensitivity of the prox. sensor, but can't seem to figure out exactly what causes the sensor to trip.

I currently have the "warn away" set at most sensitive. If I walk around the car (within a foot), it SOMETIMES chirps but not always. Shouldn't it consistently act the same way?

Does the prox. sensor continuously check for motion within its perimeter, or does it only check every couple of seconds?

SOMETIMES I can reach into the car and the sensor doesn't trip at all. What exactly causes the sensor to activate?

Am I right to adjust the sensitivity settings with the top down?

Thanks...

 

Sorry, intended for the electronics forum...

 

Moving to Electronics..

 

I've copied some text from a long boring write-up I did a while back for something else, but it explains the "proximity sensor" idea.

In general, they are "looking" for motion all the time, but it's likely that they will be more sensitive (easier to trip) if allowed to "settle down" after being activated (60 seconds maybe?). Commercial devices that are similar in operation will automatically decrease their sensitivity if there is constant motion, but I doubt a car sensor is that sophisticated. It might, however, have a time delay to keep it from tripping more than once a minute or so, and you might try another walk test with long pauses between trips.

After reading the below stuff, you should understand why the mounting location of the sensor is critical for it's operation, and that it's going to be difficult to find a spot that works well for all situations. You might want to try moving the sensor around and do some more testing.

These devices are not proximity detectors at all (there are such things) but "proximity detector" sounds fancier than "motion sensor" so that's how they are marketed. If it was a proximity detector it would be more likely to trip at the same distance from your car. And true proximity sensors don't care how slow or fast you move (your device will) - if you are at the trip range it's an alarm, no matter how long it took to get there. Car "proximity detector" devices are usually microwave Doppler shift sensors. That's fancy talk for a radar transmitter/receiver combination that detects motion.

What

 

Modifry,

Thanks, that's exactly what I was looking for!

I had turned the sensitivity up just for testing purposes, and think I have it where I want it now (much lower). The only time I want it to chirp (warn away) is if someone is either touching the car or has put their hand in the cockpit. Let 'em look from 2-3 feet!

It seems like there are just a lot of variables that affect the sensitivity, so it's hard to get a 100% repeatable test. The whole goal was to make sure that it wasn't going to chirp just because someone passed by.

At least you can adjust the sensitivity for chirping (warn away) and the actual full-blown alarm.

I've turned it down a few notches, so we'll see if it's too sensitive.

 

It will also change its sensitivity depending on outside temps. This gets quite annoying. I have had to adjust mine throughout the year due to the temperature changes.

 

This would be very unusual for a microwave device, since it does not use air as a transport medium (radio waves travel just fine in a vacuum). But now that I think of it, it's probably the module itself (the electronics) being affected by temperature, which is another indication of a not-so-sophisticated device. Of course no one wants to pay $300 for a motion sensor for their car that's the size of a shoe box, do they?

Now I do believe it would be affected by extreme humidity changes too, since the water in the air will absorb/reflect the signal somewhat.

 

I have a very hard time adjusting mine so it will warn at all with a 'reach hand into car', but not warn all the time with 'parked top up and wind/loud truck vibrates top'.