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Keyless entry fobs result in rash of vehicle thefts

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I can't say I understand this 100% (Score: 1)

by tanuki64@pipedot.org on 2015-05-11 16:49 (#8TZY)

Ok, the car sends constantly some kind of 'hello' signal. Usually it has a reach of 30cm. Fine. The amplifier increases signal tremendously... understood. But now the key has to 'answer'. And its signal is not amplifies. So how far away its signal can be detected by the car? And where is the problem to limit this reach to perhaps 1m? Then the thieves you need two amplifier... And a way to get close to the key without the owner noticing it.

Re: I can't say I understand this 100% (Score: 1)

by evilviper@pipedot.org on 2015-05-11 19:00 (#8V64)

No doubt the signal boosters/amplifiers in question are bi-directional.

There is no way for a radio signal to be limited to any specific range. The typical working distance is based on the common antenna configuration(s). Using a highly directional (high gain) antenna, you can reach a signal from many times further away than it was ever designed for. For example, how many people are stealing distant neighbor's WiFi, thanks to a Pringles cantenna, or similar?

Re: I can't say I understand this 100% (Score: 1)

by tanuki64@pipedot.org on 2015-05-11 20:38 (#8VC1)

Sure, the amplifiers are bi-directional, but even such amplifiers have limits. If the normals distance is 30cm, you go within the 30cm range of the car and maybe amplify it to 100m. No problem. This I understood. But an amplifier can only boost what is receives. How far are key/car usually apart. when the car is parked and the owner at home? 20m? 40m? You say there is no way to limit a radio signal to a specific range. Of course not. But when the strength of the key signal is too weak to be detected by the amplifier in 1m distance, it effectively is limited. So, why is the signal strength of the key so strong, that the amplifier can receive and amplify its answer over such a large distance?

Re: I can't say I understand this 100% (Score: 1)

by kerrany@pipedot.org on 2015-05-11 20:59 (#8VD2)

The idea that the key is constantly generating a signal is a little difficult to believe - receiving signals is cheap, battery-wise, but sending would surely wear that sucker out in a year or less. More likely it only 'wakes' when it detects a ping from the car that passes whatever authentication it has built in, probably with some form of RFID passive receiver. Thus the car is doing the generating, and the thieves have access to the car because it's parked on the street or in a driveway.

The scenario goes something like this. The thief pulls up to the sidewalk in getaway car and hits the button. The amplifier amplifies the signal the car is constantly sending to the key. The key responds to the amplified "Key where are you?" signal with its usual "Itsa me, the key!" signal, et voila, the car is unlocked.

Surely it wouldn't be that easy, but the evidence seems to suggest it is. There seems to be no validation beyond sign and countersign. Maybe they'll patch that up by adding more tests to the car's routine, but the key is probably always going to be a dumb device (unless they make it a smartphone app) due to battery life.

Re: I can't say I understand this 100% (Score: 1)

by tanuki64@pipedot.org on 2015-05-11 21:17 (#8VEJ)

The key responds to the amplified "Key where are you?" signal with its usual "Itsa me, the key!" signal, et voila, the car is unlocked.
Yes, of course... But the car has the megaphone, not the key. The key might answer "Itsa me, the key!", but why can it be heard of such a distance?

Re: I can't say I understand this 100% (Score: 0)

by Anonymous Coward on 2015-05-11 22:31 (#8VHD)

The device is bidirectional. It catches the reponse from the key then passes it to the car. Think wireless repeater.

Re: I can't say I understand this 100% (Score: 1)

by tanuki64@pipedot.org on 2015-05-12 00:46 (#8VQ5)

Didn't you read my post? Apparently not. I have no problems with the device being bidirectional. But a repeater cannot repeat what it cannot receive. The thieve stands with the amplifier by the car. The cars sends its request. According to the article this signal it is so weak that it can only be received by the key when the key is in 30cm distance. The amplifier boosts this signal so it can be received by the key in 100m distance. Fine. The key might happily answer.... 100m away. But what good is this, when the key signal is also so weak that it can only be received in 30cm distance?If the key signal is too weak to reach the amplifier, it cannot be amplified. Bidirectional or not. Is this so hard to understand?

If the key has a reach of 30cm and the car has a reach of 30 cm... where do you place the amplifier that it can amplify both signals? Either the answer signal from the key is by far stronger than that of the car. Why? Or the amplifier is much more sensitive and can receive the car and/or key signal over a much larger distance than the key can, but this is info missing in the article.

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