Passive Bluetooth Keyless Entry System

Modern smart keys allow you to keep the key fob in your pocket or purse while you simply grab the handle and tug the door open. [Phil] decided he would rather ditch the fob altogether and instead implemented a passive Bluetooth keyless entry system with his Android phone. It’s probably unlikely for car manufacturers to embrace phone-based keys anytime soon, and [Phil] acknowledges that his prototype poses a landslide of challenges. What he’s built, however, looks rather enticing. If the car and phone are paired via Bluetooth, the doors unlock. Walk out of range and the car automatically locks when the connection drops.

His build uses an Arduino Mega with a BlueSMiRF Silver Bluetooth board that actively searches for his phone and initiates a connection if in range.  Doors are unlocked directly through a 2-channel relay module, and an LED indicator inside the vehicle tells the status of the system. A pulsing light indicates it’s searching for the phone, while a solid ring means that a connection is established.

We hope [Phil] will implement additional features so we can make our pockets a bit lighter. Watch a video demonstration of his prototype after the break, then check out the flood of car-related hacks we’ve featured around here recently: the OpenXC interface that adds a smart brake light, or the Motobrain, which gives you Bluetooth control over auxiliary electrical systems.

17 thoughts on “Passive Bluetooth Keyless Entry System

    1. After having mine for a week, I suggest skipping the breakout and going straight for the chip. It’s a much easier impulse buy at less than half the cost and you really only need to connect GND, power, enable, and the speakers. If you want to get real fancy, there’s UART (2 pins), a mic, and a mode pin, but the difference in footprint makes the board not worth it.

  1. It’s not such a stretch for auto manufacturers to embrace it…you can already get home deadbolts that use Bluetooth:

    It has an app that you can use to share virtual keys with anyone else who installs the app. You can give a one-time-use key, permanent keys, or even recurring limited-window keys so that your maid or babysitter can get in when appropriate, but can’t come back at midnight and help themselves.

    A lot of those ideas would be well suited to a car as well. Friend wants to borrow your car? You can send him/her a key by email that will only work for the time you allow, and you could even tie in a GPS location and shut the car down if they try to take it outside of the agreed upon area.

  2. A couple questions about this:

    I’m assuming the arduino/hardware are wired to a constant 12v from the car battery with a 12v-to-5v converter. How much electricity does the entire project take per day?

    Also whenever you exit the app, it doesn’t activate the bluetooth. How is this practical in a sense that you always have to take out your phone and open the app to get the car unlocked?

    1. 1. According to his website, it draws 25 to 42mA (though that may be just the Bluetooth module).

      2. I think the app was just for demonstration/visualization, though I could be wrong. I’m not sure exactly what the app is doing that differs from simply leaving the phone’s Bluetooth on.

      1. hey josh,
        I’m Phil…(the author)

        1.) those figures are roughly correct. When actively connected I measured 35 but it varies with range between the antennas. The BT module will adjust its output power and lower it when you are very close.
        with the arduino, which is also running a lot of other stuff in the car, I am drawing around 150mA, which is a tad high but improvements are on their way.

        2.) The app is absolutely necessary as it opens the sockets for the BT to connect to. Without the app the serial profile communication is not possible (that was with Android 4.1)

        1. Hey Philipp,

          It’s Mark from Bluetooth Keyless, keep up the good work. Just for a comparison on current draw, our units are less than 10mA at idle and roughly double that when transmitting full operating range, so you should be able to trim the current draw down a little more on the BT side.

          Stay in touch and best of luck!

  3. Bluetooth packet dumps or smartphone binaries are easier to reverse than a passive RFID with proprietary encryption..

    In this case you hardwire the most secure part of the car security in, so an attacker only has to deal with the weak element to defeat all security..

    Of course nobody cares about the common persons car that much. You’d want to make it so the transponder doesn’t allow someone to just pop the ignition lock and drive away though..

    1. Exactly, things like this are known to be weak points, but as its very unlikely that a car will have this, no theif is going to try and attack it.

      As you say, the issue here is to ensure that it doesnt give easy access to wires/relays etc for theifs that wouldnt be possible otherwise.

      I would be interested in implementing this on my car too! :)

  4. I have a tesla and it allows me to unlock the car with my phone. I don’t even have to take out the phone or run the tesla app. I simply walk up to the car and pull the handle. Somehow the car detects my phone bluetooth and unlocks. do you have any idea how it’s done? Your implementation requires you run the app but theirs seems to be native to the phone.

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