Thieves Turn To Bluetooth To Identify Cars Containing Satnav

[Aspectcarl]

Modern consumer devices as described in this article use microcontrollers or custom controllers, these components use a reference clock for timing, when a consumer device as described is in sleep mode the reference clock is still running; albeit at a reduced frequency and a reduced power.

A scanner is a wideband receiver and can be tuned to the fundamental frequency of the reference clock or a harmonic of the reference clock. However there are several points that need to be observed when considering whether a scanner is an effective tool to determine if a vehicle contains a sleeping consumer product suc as a sat nav or laptop.

What are the background noise levels at the selected frequency, how experienced is the user at operating the equipment and discriminating the results, how effective is the non directional antenna, what other noise sources are nearby and how effective is the vehicle's bodywork at shielding the reference clock.

In all likelihood detecting a sleeping device is unlikely, detecting an operating device such as laptop is possible and easy, as an experiment try placing your fm radio next to a computer or laptop and see what comes out of the speaker, you may need to tune to a weaker station in some cases.

Turn your laptop off and repeat the experiment, the result should be zero interference.

The next question is whether a sleeping device is still transmitting the 2.4ghz Bluetooth carrier, as has been pointed out there is no Bluetooth presence Therefore other receivers have detected that there is no carrier, if there is no carrier there is nothing for the scanner to detect.

So is a scanner a useful tool for detecting sleeping consumer products? In certain cases a scanner could be used, although the user needs to be experienced in determining what the scanner is producing and how to discriminate between a sleeping sat nav and a sleeping vehicle body control module.

Can a scanner be used to detect sat navs or laptops in operation? Yes, less discrimination is required, effective sweeping of a vehicle could take place fairly quickly, if the the device is running then it is also likely to be producing a Bluetooth presence. The Bluetooth label will also be useful for indicating the device type.

Does a powered down device transmit a detectable reference clock? Yes it does, typically a real time clock device continues to run so that device can continue to keep the system time and date, although it is in the kilohertz region and will be a very small signal requiring the scanner to be placed at a specific part of the product and will not detect this signal anything further than a few inches away.

It is likely that the thief had a hunch, or had been watching the owner leave the vehicle or was relying upon on the fact that most of us are just plain lazy and think our valuables are safe in a locked vehicle.

[psyskiesman]

Why did the thieves walk past all the other cars and stop at my friends? Why did they force open the boot? Why did they "discover" the laptop hidden under the coat? All within 19 seconds! Hunch? I think not; the scanner was definitely used as confirmed by the police!

[Aspectcarl]

Can you prove the scanner was used in this crime?

[psyskiesman]

This crime was committed in Leicester about 18 months ago. The friend was actually my supervisor at work, but he has now left the company, so I am no longer in contact with him. He did say at the time that the police had studied the cctv footage and confirmed it was most likely that the perpetrators did use a scanner.

[Aspectcarl]

The criminals had a scanner, they were seen using a scanner and they broke into a vehicle and stole something, but what evidence is there other than circumstantial that the scanner led the the criminals to deliberately target that vehicle in preference to other vehicles nearby?

[PaulB2005]

Until someone confirms what this scanner detects from a switched off device I'm not convinced.

[Aspectcarl]

The scanner may or may not give an indication of a signal, the signal is likely to be other devices; possibly part of the vehicle or background noise. Typically a device turned off also turns off it's reference clocks. Therefore any indication produced by the scanner is false. You can't detect a carrier from a device if the carrier isn't being produced, be that an intentional or unintentional carrier.

There are some devices such as sat nav units that keep the gps receiver powered to enable a faster start up time, so not all devices turned off are in fact off.

Even under these circumstances a scanner would not be able to detect any electrical activity because of the device type, the distance between the device and scanner, the shielding effect of the bodywork and the antenna type. To reliably detect any form of electrical disturbance i would expect to use a close field probe and be using it inches from the device.

In summary a scanner would be useless for devices that are turned off, and a device that is standby mode and has remained asleep while the scanner was being used.

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