Cell phone entry to a locked car

Recently,I’ve got again in a situation where I’ll go’round my car helplessly, unable to get in and take my keys ,forgoten inside.The picture attracted, as always, a crowd around, all so willing to help - with their knowledge moustly then anything else.

And there it is this middle age lady, approaching me,with the common question-“Are the keys Inthere?”-followed by-“Do You have a spare key?”.In respond of my surrprised face expression, she said that the other day her dougther make her press the unlock button of the spare key set at home in front of the cell phone microphone,while the smart girl broght her cell phone close to the drivers door. I haven’t had a chance to try that technique,but wonder is there a solid ground behind that “fact”?

About 2 years ago my dear wife called me on her cell phone.

Wife to hubby: I’m at Costco & I just locked myself out of my car.

Hubby to wife: How in the world can you get out of the car,close the door, press the lock button on the remote AND lock yourself out of the car.

W to H: Thats not how I do it, I prefer to open the door, press the lock button on the door & then close the door.

H to W I shoulda known.

Try this, hold your cellphone up to the drivers window.

I held the remote up to the phone & pushed the unlock button.

No joy & I ended up driving to Costco.

That night I took a quick look at the wiring diagrams & found that the receiver for the keyless entry is behind the center section of the dash.

Held the cell phone in that area & tried this little experiment again.

Even under this ideal setup the doors would not unlock.

So on my wifes 02 Sonata this little trick definetly does not work.

Looks like the phone lines are not able to transmit the high frequency that the keyless remote operates at, so I dont think this will work on any car.

Most keyfob remotes use RF frequencies to communicate to the receiver in the car. Some use a infrared light signal. In either case, a cellphone is unable to re-transmit signals like that. It is designed to pickup a limited range of audio (voice) frequencies through the microphone and transmit them.

GM vehicles which use the OnStar system have the ability to remotely open doors and other things like that. This is a cellphone system also but it is a different design than the normal hand carry type phone since it is integrated to work with the car systems along with making normal calls. Perhaps this is why some folks think that a normal cellphone will repeat a keyfob signal.

I don’t know if your vehicle s a GM or not, but nothing but the right transmitted radio frequency aimed at your vehicle will ‘remotely’ open it.

The radio frequencies are constantly changing.

I always carry a spare ignition key. (properly programmed of course)


The radio frequencies are constantly changing. I always carry a spare ignition key.
The remote entry receiver in the car must store as many (constantly varying) frequency codes as there are remote entry keys for the car. The keys are not kept in sync. The maximum number of remote entry keys per car is about four.

BTW, one way of getting the key transmit/car receiver frequencies out of sync is by pressing the key when the car is out of radio transmission range. There are work-arounds for this, provided the number of key pressings is not too large. But if the number of key presses with the car out radio range is large enough (256? 512?), the key won’t work anymore. Try it!