Ever wonder how that ‘twit–twit’ door locking mechanism (keyless-entry remote control) in your car work? I did… This post is inspired by a someone who stupidly thought that you can unlock a car with the key (unlock) miles apart by using a cellphone! Yeah, how dumb is that?! Imagine you lock your car keys inside you car and the spare key is in you house several miles away. You then asked your wife to call you and ‘twit-twit’ or unlock the car by using the cellphone. He hopes that the sound will be loud enough, coming from the earpiece of the phone, to unlock the car!

Of course it doesn’t work that work that way. By inspection you’ll instantly know that it has something to do with RF or radio frequency. Let’s read more shall we?

How does it unlock the door from 20 feet away?

How secure is it? Can I open someone else’s car with it, or can other people get into my car with theirs?

That keychain thing with your key is that locks/unlocks your car is actually a radio transmitter. When you push a button on the fob, you turn on the transmitter and it sends a code to the receiver, which in turn, locks or unlocks the door.

Now the second interesting question:

In the very early days of garage door openers, around the 1950s, the transmitters were extremely simple. They sent out a single signal, and the garage door opener responded by opening or closing. As garage door openers became common, the simplicity of this system created a big problem — anyone could drive down the street with a transmitter and open any garage door! They all used the same frequency and there was no security.

By the 1970s, garage door openers had gotten slightly more sophisticated. You can see this level of sophistication in the photos below. The first shows a controller chip (black) and a DIP switch (blue). A DIP switch has eight tiny switches arranged in a small package and soldered to the circuit board. By setting the DIP switches inside the transmitter, you controlled the code that the transmitter sent. The garage door would only open if the receiver’s DIP switch were set to the same pattern. This provided some level of security, but not much. Eight DIP switches provide only 256 possible combinations. That’s enough to keep several neighbors from opening each other’s doors, but not enough to provide any real security.