Adding Motion Sensor to BMW Alarm

Here is what I did – it is fairly straight forward but please make modifications at your own risk.

The sensor I used came from Sound Conceptions – “”. The sensor is listed as “sensor: single zone perimeter sensor (radar)” and is $24.95 as of today (3/30/98). You can find it in the storefront – security section. It has three wires to hook it up – battery, ground and trigger. The wires are just long enough to reach where I mounted the sensor. If you want to experiment with different mounting locations, you may want to extend the wires.

For safety, unplug the BMW alarm harness at both ends before making any connections. I soldered and taped all connections.


connect this to the fused battery wire in the alarm wiring harness this is a yellow wire with an inline fuse. Connect to the alarm side of the fuse, thus the fuse protects the new wiring.


connect this to the ground wire in the harness – brown wire.


this will get connected to the hood switch sensor wire (white with red stripe) in the wiring harness. To avoid potential interference between the new and old sensor – I isolated them with two diodes. The diodes are 1N4001 which you can get at Radio Shack. Cut the existing sensor wire and splice in a diode with the cathode (banded end) toward the sensor – this sensor is active low. On the alarm side of this diode, add another with the banded side toward the new sensor – connect the new sensor trigger wire to the cathode of this diode. See the crude diagram below:

I mounted the sensor in the console just forward of the gear shift. Remove the gear shift boot and the foam insert. If you put just the hook portion of some stick on velcro tape on the back of the sensor, you can stick it to the carpeting under the console. You will want to play with the sensitivity adjustment on the sensor. I have mine currently set about 3/4 of the way to fully sensitive.

Performance is good but a little inconsistent. If someone sits in your car, the alarm will definitely go off. An arm reaching in will set off the alarm if the arm is moved around. Repositioning the sensor might help – the directions say the higher it is in the car the better.

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Clifford IQ-800 Car Alarm

Pros: Motion Sensitive, Duel Zone Warning, Keyless Entry, Expandable, Brand Name
Cons: Expensive, Non BMW (Voids Warranty?)
Cost: $500 Installed

Part of the down side of having a really cool car is that it draws a lot of attention and some of this attention is from car thieves, car stereo thieves, and vandals. With top-down weather approaching I decided the roadster needed a car alarm, a really good car alarm. I started my shopping/analysis the same way I start most of my research by establishing a list of rules that my future car alarm must adhere too. Hereafter referred to as “Robert’s rules for car alarms”.

1. Budget – $500 This is double my insurance deductible so the alarm must deter a thief twice in it’s life time to pay for itself.

2. Keyless Entry – Because I’m lazy

3. Motion Sensitive – Glass breakage is all but worthless in a convertible.

4. Duel Zone – For the gawkers that get a little to close the car it must warn them without the alarm fully going off.

5. Must Open Garage Door – So I don’t keep a garage door opener in the car.

6. Flashing Red Light – For extra top down protection.

7. Auto Code Switching – So no one can steal the code.

8. No annoying “Chirping” every time I hit a button – Like for this to be an option I can turn off and on.

I also established a second set of rules because I decided that my wife’s car should also have a car alarm.

1. Budget – Additional $500 (double the deductible)

2. One remote can work both cars – In case the wife wants to drive the roadster.

3. Remote headlight activation – She parks in a parking garage.

4. Easy to use – I’m a computer nerd, the wife is not.

Turns out this is a very picky list. I only found one company that could pass all 12 rules. Clifford makes a line of car alarms called the intelliguard series. The Clifford Intelliguard 800-IQ was a perfect match for the roadster, and the Clifford Intelliguard 700-IQ will work nicely in the wife’s 318i. However, I had to deal real hard to stay within budget.

The total price for this pair of virtual watch-dogs was just over thousand bucks. The 800-IQ Cost $500, the 700-IQ Cost $400 and the garage door opener was another $100 (prices include installation but not sales tax). It has taken some adjusting, but both alarms are working great. The first day or two the 318i had a few false alarms but with a few clicks of the remote I adjusted the sensitivity down. The roadster gave me a little more trouble, and ended up having to go back to the installer for help. They relocated the sensor and that made all the difference. Now if you get with six inches of the cockpit (top up) or nine inches (top down) the car will chirp at you. Cross over into the cockpit and the alarm will go off.

I’m very happy with both alarms, but here are my very picky complaints.

1. Alarm could be louder.

2. Motion is only detected around the cockpit and truck area. The motion sensor gets blocked by the dash and fire wall.

3. The motion sensor is not flawless, it needs to be adjusted a couple times a year.

Despite these picky complaints I am very satisfied with my purchase. The piece of mind (especially for my wife’s safety) makes this upgrade an excellent value.

Follow Up: Motion Sensor Location – I have received several e-mails asking about the location of the motion sensor. The key thing about the motion sensor is that it doesn’t do very well around metal. After trying several locations, I found a spot under the armrest (about where your forearm rests) where there is very little metal. You will have to take out the armrest/cupholder and fish the wires back to this location, but it is pretty easy to do.

Additional Sensors: I found out that additional sensors could be added to the Clifford rather easily. So besides the motion sensor that initially came with the IQ-800 I added a shock sensor to detect impact (like someone bumping the car) and a tilt sensor in case someone tries to tow the car or jack it up to steal a wheel.