car alarms

[tico1967]

does any body knows at what frequency does car alarms and the signal for unlocking the car doors work under.

 

[blueroomelectronics]

Could be quite a few. The carrier alone won't unlock the door, encrypted digital data is sent along with the carrier.

 

[picbits]

It depends on your country.

Generally 315Mhz to 950Mhz (ish)

 

[JimB]

The plippers for my two cars operate on 433.92Mhz.

JimB

 

[picbits]

When replying here, can you be aware of a new spate of crimes involving jamming remote locking signals .........

 

[JimB]

When replying here, can you be aware of a new spate of crimes involving jamming remote locking signals .........

Would you care to elaborate on that?
Some little scrote has a transmitter running on 433.92Mhz to jam the signal, or a perfectly legal signal swamps the receiver and my car does not lock, I just use the key. The same as I would do when the battery in the plipper goes flat.

JimB

 

[picbits]

There have been a few instances of people thinking they have locked their cars with the keyfob but either outside interference (i.e. radio masts or deliberate jammers) have prevented the cars from locking. The owner has returned to find their car with the doors unlocked/open and the contents of their cars missing.

I was observing a few people in the local Tesco car park the other day and the majority walked away from the car pressing the keyfob and not checking to see if the car had actually locked .....

 

[Mickster]

does any body knows at what frequency does car alarms and the signal for unlocking the car doors work under.

I can understand picbits' concern and the OP's wording leaves a lot to be desired...

 

[Brian Hoskins]

I did some experiments with my girlfriend's keyfob and found that if I captured the data sent by her key-fob, and then simply re-transmitted it to the car at a later time, it would operate the door locks! Although only for that one instance. Further attempts to operate the doors with the same data failed - the key must change after that.

If she locked the doors, I could un-lock them. Similarly, if she un-locked the doors I could lock them.

Quite a security hole if you ask me!

I only did my experiments out of interest. I have no desire to hide in the bushes waiting for someone to press their key-fob to lock their car so that I can return after they've gone and un-lock it. But I'm sure there would be those who *would* take advantage of such a security hole.

It's likely that similar security weaknesses no longer exist on newer vehicles though...

Brian

 

[Mickster]

It's likely that similar security weaknesses no longer exist on newer vehicles though...

Brian

For quite some time now, rolling codes have been used on newer vehicles, but they are not without their own problems.

Complex algorithms are used on the receiving end, which anticipate a sub-set of codes to be expected from a valid remote based upon the last code sent. This generally allows for inadvertent key presses whilst the remotes are in a handbag or pocket, for example, or wandering around a car park pressing the remote when one can't remember where the car was parked.

But sometimes, whilst out of transmitting range, a frustrated infant/toddler being 'entertained' with a bunch of keys can activate the remotes enough times for the transmitted code to be far out of the expected range of codes and result in the remote losing sync. This is not only frustrating for the parent returning to the vehicle, to find the remote inoperative and have to open the vehicle manually, but for the service staff too since they usually end up wasting time simply re-syncing the remotes.

Some manufacturer's engineers have updated the DTC's (Diagnostic Trouble Codes) now, adding the text "May set when used out of range" for some remote fault symptoms.

 

[shimniok]

Interesting... something to be said for the 2-way alarms I guess...