Super Mcguyver Tip: Unlock Your Car Through Your Cellphone

[thebobman]

Holeee-shit that is some ridiculously cool and potentially super handy shit:

I imagine this will come in super handy when 4 of the 6 people you took to apex are already at your car and you're off talking to the grass 3 miles away.... 5 hours after the last DJ stopped playing... while its raining... and 2 of the people are in full-on fun-fur candy raver gear...

[project.one]

Not bad!
So noted!

[mapleleaf4ever]

Saw this on digg.

Pretty damn cool!

[Goodfellow]

I can NAT! believe you can unLACK! the car with the key FAB! like that.

[liquidblue]

WOW! Sweeeeeet find. That is super cool.

Anyone with a technical explanation? I think I understand how this is working but if some one knows for sure please explain.

[thebobman]

Super-simplified technical explanation (Skip to end for Uber-Simplified explaination):

Step 1. Signal Input into the Cellphone:
The Microphone in your cellphone consist of three things:
1. A thin piece of plastic or light metal that is compressed by the change in air pressure as you talk at it.
2. That piece of plastic covers a coil of copper wire which is moved up and down by that piece of plastic.
3. A tiny magnetometer which senses the magnetic filed generated by the coil of wire moving up and down.
Your talking moves #1 which is connected to #2 creating a changing magnetic filed which is picked up by #3.

The key fob emits a unique radio frequency. Radio signals are essentially electromagnetic waves, which means they can be picked up by magnetometers like the one in your cellphone. So the radio frequency from the fob creates the changing magnetic field and is picked up by #3, the magnetometer.

Step 2. Signal Playback out of the Cellphone
The speaker in your cellphone is exactly like the microphone, except that instead of having a magnetometer that detects the coil of wire moving there's just a magnet. Running electricity through the copper coil changes its magnetic field and since the magnet in the speaker wont' move, the coil moves up and down against the piece of plastic creating changes in air pressure, aka sound.

The key fob's radio signal gets picked up by one cellphone and at the other end the signal is run through the copper coil of the speaker just like a normal call. The frequency of the electromagnetic radio signal produces a sound well above human hearing capacity, but it also moves the coil of copper up and down recreating the electromagnetic signal that the other cellphone picked up.

Uber-simplified explaination:
The magnetically sensitive microphone in your cellphone picks up the radio signal of the key fob and transmits it. At the other end the speaker in the other cellphone tries to reproduce what it thinks is audio, but in doing so the copper coil in the cell phone's speaker recreates the electromagnetic wave the key fob first put out.

There's a good chance that the signal is actually several radio frequencies and the one that the cellphone is picking up is just has a shorter range than the rest of the signal.