According to my local news a guy built a device which disabled garage door remotes and key less automobile entry fobs in an unspecified area. He said there was no malicious intent. So what did he build?
Dennis
Some kind of replay attack Replay attack - Wikipedia - the device receives nearby signals from keyfobs, and plays them over and over again, which the vehicle interprets as an attempt to break into the car - which results in the vehicle disabling keyless entry until the owner uses the physical key.
That’s my guess
Wouldn’t that make it hard to claim it was not malicious?
Dennis
Could be a side effect of something not malicious (or I could be wrong in my guess).
I suspect that it was just some type of radio transmitter.
Most keyless entry devices operate in the same band - 315MHz.
If our budding radio engineer was working on a home-made transmitter that either operated in that band, or had a powerful harmonic in that band, it could interfere with other devices.
That’s my guess, too. It doesn’t matter whether a signal is digital or analog, it still has to be sent over a frequency. And 315 mhz is a doozy.
The very first one is for a ground penetration radar system.
Theoretically, it might not even be intended as a transmitter at all. Pretty much any electronic device will produce some radio interference, if it’s not properly shielded. Though for something not intended as a transmitter, the area over which it’d be significant interference would probably be fairly small.
he might have made a radio repeater and it messed with rolling code devices.
The story was in some papers today. This is a Toronto Star feed from the NYT:
None of these descriptions give any indication of what type of device it might have been, why he would design it that way, or why it would have to be so powerful that it would effect fobs and garage doors for such a wide area. Couldn’t a basic, commercial motion detector have service this purpose?
There’s the apocryphal story that when the US president comes to town, funny things happen. (not just those) Garage doors fail, etc. The suggestion is that a bubble of radio jamming follows the president while on the move; for example, many years ago the president of Pakistan’s convoy drove over a bridge- and when he was a decent distance past, a bomb planted under the bridge blew up. Speculation was he was travelling with a cellphone jammer and the cellphone trigger signal was received after the jammer had left the area instead of when the vehicle was on the bridge.
Why did some guy build a electronically noisy transmitter? Because he could.
@ guizot - I read a few stories on this because, like you, I was curious about the reasons. The level of detail between the stories varied quite a bit and a couple added a lot more detail.
My impression was that he was a retired electronics guy (he’d maybe worked for an electronics company?) He liked to tinker and basically McGyvered this motion sensor out of old parts he had sitting around his shop.
I didn’t get the impression he “designed” it to give off the 315MHz signal, that seemed to be an unintentional by-product of the battery system he was using. He had no idea it was emitting that signal. (Or if he knew, he had no idea the frequency was jamming devices)
The dude I’m imagining is like my father: “Dad, you know you can go to the hardware store and buy X? You don’t need to cobble it together from workshop junk”. This was inevitably followed his silent stare, implicitly saying “Why would I spend good money to buy something I can cobble together from all these resources I’ve been saving for all these years?? You idiot, have you learned nothing??” 
I’m not quite having the same conversations with my son, but probably soon will be as the saved resources in my workshop slowly expand and I look for opportunities to use them.
[quote=“md2000, post:11, topic:833477”]
… many years ago the president of Pakistan’s convoy drove over a bridge- and when he was a decent distance past, a bomb planted under the bridge blew up. Speculation was he was travelling with a cellphone jammer and the cellphone trigger signal was received after the jammer had left the area instead of when the vehicle was on the bridge. … /QUOTE]
You’re not thinking of this incident, are you? Good story but not on the surface related to the matter under discussion: