Front door idea?

I have no idea where to ask this so here goes…

I am tired of opening my front door rather finding my keys. I want to make a front door that unlocks when I walk up to it like my car does. and I want the front door to recognize my car fob so I don’t have to carry a pocket full of fobs. Is this too much to ask?

So my question is … does anyone know how the car fob works? I assume each fob transmits a code that is recognized by the car. How is it transmitted? How can I capture this code ? If I can capture the code I can make ,using a photon , a device that will unlock my door?



Using your car key is probably not the best idea. You can’t easily authenticate the key because it’s not meant to be duplicated except by the car manufacturer. Otherwise, anyone could buy a Particle/Arduino/RPi/etc and steal cars by duplicating the RF signals. There was a project I found that was able to read the key’s serial number and tell which buttons on the keyfob were pressed… but the authentication part is encrypted and cannot easily be decoded.

An excerpt from this project:

It was an interesting project to figure out how the remote keyfobs transmit the data, but it cannot be used for anything important. The keyfobs can be identified by their serial number and the code knows which buttons were pressed, however, since the encrypted part cannot be decrypted without a decryption key, the keyfobs cannot be authenticated and the receiver can never know if the received key code is authentic or fake.

So if you could build a system where you were able to detect the SN of the keyfob, would you really want to leave yourself open for a savy hacker to break into your house?

There are other options here outside of building your own keyfob detector. I have Schlage ZWave deadbolts and an ISY944i home automation controller. The deadbolt connects to the ISY via ZWave and the ISY has IFTTT/Amazon/Google integrations. I can use my smart phone to unlock the house when I enter a geofence as well as other options. I do not have this enabled. If you wanted to integrate some method of using a Particle device, you could use the IFTTT integration to do just about anything you want.


does the fob emit a continuous rf signal or utilize an rfid that signals only when close?

I don’t see the insecurity issue. To break into the house they would have to steal the rfid signal, decode it. no less secure than my car. Am I missing something?


There’s not a whole lot of information about the specifics of how automotive key fobs work… for good reason. I’m talking about push-to-start or keys with an embedded chip. There are also plain old push button key fob that unlock the car. For the embedded chip keys, most likely the car sends out a periodic beacon and the key fob responds like RFID. That project link I posted was talking about garage remotes but the concept is the same. You might be able to read the SN from your key fob. But if you can read that SN using an NFC antenna or something similar, then a hacker sitting in a car across the street with an RF sniffer and a Pringles can (which is a makeshift directional antenna) will get that SN also. If the hacker gets it, they can emulate your key fob and gain access to the car/house.

Automotive key fobs should have an extra layer of security. There is an encrypted private key somewhere that you cannot easily crack. The car receives the encrypted key and decodes it verifying that the key fob is authentic. I’m no cryptographic expert but it would probably be the same for sniffing TLS packets on a network. You can see the host IP and MAC as well as the destination. But the payload is encrypted. You can’t easily grab that packet and make it look like it came from you instead of the original sender.

There are news articles about this kind of theft and the auto industry is always playing catch up.


I recommend these.

I haven’t carried a house key in 10 years. Just make sure you change the battery as soon as you get a low batt indicator. Or, as I do, put one on your back door so there’s an alternate if the batt dies. Only complaint is it is only a 4-digit password; it should be longer.