Car security solution - designing the right motion detector

Question

My car gets broken into quite frequently. The car is right outside of our bedroom window. The break ins happen at night, and we never hear them! They must be very sneaky.

I would like to design (or find a plug and play solution) for a motion detector that I will place inside the car that is either battery powered or something that can plug into the car adapter. When it senses motion, I want it to send a signal to our bedroom window so that we can call the police.

Here's an amazing diagram of what I want to happen.

Can you please suggest a design or a plug and play solution that I can use to do this? I know there are many motion detectors, but I would specifically need something that will work at only a 1 meter range because it should be inside of the car sensing any movement INSIDE of the car, and ignoring everything outside.

I don't know if this is relevant, but the windows are tinted.

Answer 1

Ultrasonic sensors seem to be the sensors of choice for many car alarms. You can often buy electronics kits which use ultrasonic sensors to detect motion. The outputs are often simply in the form of a relay, so you can connect it to almost any other device you can think of. Google around for 'ultrasonic motion detector electronics kit'. There's a bunch to choose from.

Simply mount one of these inside the car, and wire it up to the 'deterrent' transducer on the outside.

Alternatively, you could simply wire it up to a wireless doorbell, and leave the chimer by your bed at night.

Also consider wiring it up to a couple of cheap little video cameras, so that you can grass up the little urchin to the police.

Answer 2

Well, let's look at the problem you are trying to solve from a simple perspective. As I see it, you need two things to happen.

1. You detect the motion
2. You wirelessly notify yourself that motion has been detected

Simple enough. Now, it depends of course on what your requirements are. Things like:

• How big you want the device to be
• How much you want to spend on it
• What kind of experience you have with electronics

You didn't provide any of this information, so I'll tell you what I would do if I were in your situation.

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Detecting the Thief

Use an Ultrasonic Sensor

Grab the HC-SR04 ultrasonic sensor. It is super easy to interface with most microcontrollers, and very accurate. Very cheap too (~$4)

Use a PIR Sensor

They are also very cheap, and as feasible a solution as is the one above. This one would be a little more compact, and have a wider field of view though. Probably a little more expensive than the HC-SR04.

Transmitting the Information

Use an xBee WiFi Shield

You'll need just one of these for your car. Hook it up to your WiFi connection, and it can send data directly to your computer or even your mobile phone if you are willing to write a quick app which can alert you.

Use a pair of 2.4GHz Transceiver Modules

You can try the cheap-o NRF24L01 modules. You'll need two, one for your car, one for your room. The main advantage is that they are unbelievably cheap (~$2.50 a pop), and there is good sample code out there too.

A Microcontroller to Process the Data and Interface With Your Components

A typical recommendation would be to use the Arduino. All the components I listed above have lots of sample code available which should work flawlessly with the Arduino. You would likely need two in any of the scenarios, unless you are up to using the xBee shield to send the data directly over your WiFi connection. I have never tried it, but it is well documented and shouldn't be very hard to do.

Or you could go the cheaper route and use a standalone AVR or PIC microcontroller. Also not a bad solution, as you can keep things much more compact and portable. If you really want to use the Arduino code, you can install an Arduino bootloader on most AVRs, or you can just code them in C. The Arduino route is easier from a coding standpoint I suppose - but that's arguable.

Power

Lastly, you'll need power. You have two options:

1. Use a battery pack. Go for rechargeable NiMh packs if you choose this route.
2. Use the cigarette adapter in your car.

Hope this helped!

Answer 3

https://www.adafruit.com/products/189

The sensitivity of these can be tuned via the trimpot on the back.

Connect to an Arduino running off a battery, or if you drive the car often, connect it to the car's battery. Then connect a pair of XBees for your Wireless communication

https://www.adafruit.com/products/128

Have another Arduino set up as your 'base station' and it can light up, make noise, etc, whatever you want to do.