Keyless entry

Lol we had one of those wirless door bells and it was the same, different frequencies (switch setting on the bell end...pardon the double entendre..) set off a different ring tone.
Was great until the people across the road got the same door bell and kept setting off a horrible tone that shouldn't off been allowed in the first place

Drove us nuts until we figured it out wondering why the doorbell went off with no-one at the door and with a horrible tune to boot

Originally Posted by Baph

Your mobile phone picks up voice frequency (VF), translates this into electrical impulses, then translates this further to radio signals, and the whole shebang is reversed at the other end.

What is the range of VF? Approx 300Hz to 3400Hz. If you include guard bands, plus overheads, it's actually sampledat around the 4kHz band. A household phone, since it relies heavily on DTMF, samples at 8kHz. Because a house phone does twice the sampling, this is why sometimes you can have a dodgy signal whilst in a call, the person on the house phone has no problems, the person on the mobile does.

OK, so now we know the theory of how phones work, what about the car transmitters? The article linked to says the transmitter uses 315Mhz. This is 315,000,000Hz. WAY WAY WAY beyond the VF range.

So, why does this work in some cases, and not in others? The reason is the pickup used in the phones to translate audio back to electrical impulses. The speaker can happily emit 315Mhz, you'll never hear it anyway, so why do the manufacturers care? If the pickup is good enough, it will pick up sounds in the frequency beyond that of human hearing. This does take a GOOD pickup though.

Tricky, in your case, the pickup simply wasn't up to scratch.

(Yes, I have used this same principal, with a very VERY good dictaphone to scare friends witless on numerous occasions - eg, they lock their car, I unlock it, leave the door open, and wait for them to realise - always in a relatively safe area)

Ok I am confused now. We tried this with no expectation of it working because it was more fun than whatever it was we where supposed to be doing, but now you're saying that this is actually possible ?

How do keyfobs work then, I assumed they used RF rather than any kind of ultrasonic (?)

Yes it's possible. It's all a matter of capturing, then playing back the frequency.

Ultrasonic or RF makes no difference, if you can catch it & play it back, you've effectively cloned it.

Since no modern locking systems for cars (that I know of) use one time entry, it's pretty simple to do.

Originally Posted by Ping

Certain central locking keyfobs set off my cheap Asda doorbell playing the ring tones no-one in their right mind would ever set it to...

So far it's whistled dixie, twinkled a little star and barked at me...



Technology's great!

lols i wonder if thats what does mine then.???? was it abotu 7 quid?

[Richie]

I find keeping a spare key hidden on the car works well...

Originally Posted by 454697819

lols i wonder if thats what does mine then.???? was it abotu 7 quid?

No, it was a VERY expensive one... Cost me billions... trillions even....


Oh alright, it was about 7 quid...