Introduction: How to Start Your Car From a Cell Phone Via GSM Relay!

Picture of How to Start Your Car From a Cell Phone Via GSM Relay!

In this instructable I will show you how to start your car from your cell phone.  I already had a car starter installed in my truck years ago but the range was terrible and you had to press the button for a precise amount of time, otherwise it would just ignore it.  So instead of pressing a button all day long from 10 feet away I decided I wanted to start my truck from anywhere in the world!

Step 1: What Do You Need?


-GSM activated relay.  This device will contain a SIM chip that can connect to the GSM cell phone network.  It's relays must be able to be activated by phone call or text message.  In my first build I used a GSM-AUTO, but found a cheaper alternative on eBay HERE for the Quad Band version (North America) or HERE for the Dual Band (Europe, Asia, etc.). it costs around $150 which has 7 relays.  Another alternative is Relay Supply or you can go directly to the 7 switch device HERE.  One relay is controlled by phone call and the rest are activated by text message.  The relays can be set as either momentary or latched.
-Car Starter Key Fob (the remote control thing on your keychain).
-12V DC cigarette power cord
-Small plastic bag or ESD bag.
-A few wires.


-A few screw drivers
-Soldering Iron

Step 2: Canabalize the Key Fob

Picture of Canabalize the Key Fob

Begin with canabalizing the key fob.  Instead of consuming one of my existing remotes, I turned to eBay.  I found the model number of mine on the back.  Its an Auto Start 05-A433.  I entered this in on eBay and up popped a bunch of used key fobs that are compatible with my system.  WARNING: Some of these remotes may look exactly like the one you want but they come in many revisions.  Some revisions are not compatible with others.  If you are not sure which to buy on eBay, try buying one new online.

You will have to sync your remote with your car starter.  As all car starters and car starter installations are different, I won't go into detail on how to do this.  Whoever installed your car starter can usually do it for a fee but I strongly recommend you google for the models manual as its a rather simple process.  It usually involves either depressing the hood pin in a particular fashion (a pin that detects if your hood is popped), or pressing a button on the side of the remote starters brain under your dash.

Now remove any screws from the case and pry it apart.  The circuit inside and battery are not secured in any way and came out easily.

Step 3: Solder the Contacts

Picture of Solder the Contacts

Find the button that corresponds to the "start" button on your remote.  Some remotes can require a combination of buttons to be pressed in a certain order, or multiple buttons pressed at the same time.  This can be accomplished by soldering up two connections that are both wired through the relay (for multiple button presses) or a capacitor can be added to time delay one of buttons.

The contact in the center of this picture is already powered.  When a user pushes the button, the connection is made between the interlocking contacts (they look like interlocking letter E's) and the starter signal is sent.  We will be soldering one wire to each corner of the contact.  This takes a great deal of precision to ensure that you do not join the two contacts.

Step 4: Solder the Power Wires

Picture of Solder the Power Wires

Next, solder a wire onto each connector that supplies power to the remote. Color coding the wires is a good idea.  This remote takes a small but powerful 12V battery.  Note that if your remote can not handle this high of voltage (some cigarette lighters can pump out around 15V so be sure that the remote can handle this), you will have to continue using the existing battery.

Step 5: Connect Power Cable to GSM Device

Picture of Connect Power Cable to GSM Device

The GSM Relay has 7 relays.  The first is controlled by phone call.  When called, the relay will open for a set amount of time that can be programmed into the device by text message.  Mine is set for 1200 milliseconds.

I would recommend wiring the power cables into the device first.  Take the 12V DC cigarette power cord and strip the ends of the cables and slide the cable through one of the ports on the side of the device.  These ports can be tightened to ensure the device is weather proof.  I fed the wire through the port closest to the power connector, but if your wires are higher gauge this can be difficult.  Consider running the wire through the far port.  The remote key fob will remain inside the device and its wires will not be run through on of the ports.

GND (ground) is clearly marked as the top most connector.  Wrap the negative (black) wire from your remote key fob around the negative cigarette power connector wire and feed it into the GND connector.  Screw it down tightly to ensure a solid connection.

Wrap the positive (red) wire from your remote key fob around the positive cigarette power connector wire and insert it into the +12V connector on the GSM device.  Screw it down tightly and test both wires for looseness.

Step 6: Connect Key Fob Start Button Wires to GSM Device

Picture of Connect Key Fob Start Button Wires to GSM Device

Next, run the wires from our "start" button into the relay controlled by phone calls.  Each relay is simply a pair, with the first relay being controlled by phone call, and the rest being controlled by text message.  Push the wires into each connector and screw them down tightly.  Remember, the remote will reside within the GSM devices case, so do not run the wire through one of the case ports.

Once this is done, consider sliding a small plastic bag or ESD bag over the remote key fob to prevent any shorts.

Step 7: Insert SIM Chip & Power Up!

Picture of Insert SIM Chip & Power Up!

Slide back the metal bracket covering the SIM chip holder to allow it to pop up.  Insert the SIM chip as shown and press it down again, securing the metal bracket to hold it down.

The GSM device has 3 LED's on it:

-One for network connectivity. This LED won't turn on for the first 10 seconds, and then will blink quite fast when the device initializes.  The rapid blinking means its searching for a network to connect to. Once it establishes a connection (this will only occur if the SIM chip is a valid one and the device is in GSM range), the light will blink much slower, indicating that the connection has been made.
-One for indicating power status (blinks regularly to indicate it is powered).
-One for indicating TX or RX.  Whenever the device receives or sends a text message/phone call, this light will flash.

Connect the device to your vehicles cigarette lighter!  The power LED should be flashing, as should the network LED.  Once the device achieves network connectivity, the flashing of the network LED should slow down.

Step 8: Program the GSM Device

Picture of Program the GSM Device

Programming the device is simple.  I have attached a PDF to this Instructable containing the instructions.  To quickly add a phone number to the list of valid phone numbers that can call the device (also called a white list), send the following text message to the device:


PWD is the password (which can be changed), and WHL01 is the first position in the white list.  If you wanted to add a second number you would use WHL02, etc. and so forth.

The phone number to be entered should contain the area code and regular phone number with no dashes.  Occasionally the international country code must be prepended to the start of the number, but try without this first.

Call the device and the first relay should loudly clack open and closed for 300 milliseconds (default length of time).  The device will never pick up the phone call; rather it merely checks whether that phone number is in its white list, and then either ignores it or acknowledges it.  It usually activates itself on the second ring and causes you to hear two rings to occur quickly one after another when it activates.

To update the length of time to one second, use this command:


Figure out how long you normally have to press the start button for to start your vehicle and then program the relay to open for the proper amount of time.

Step 9: Test It Out!

Picture of Test It Out!

Time to test our device out.  Call the device and watch as the TX/RX LED activates.  The relay should loudly flip open, and if you have a small LED on your key fob like mine, you should see this glowing as the "start" button is pressed by our relay.  If the timing is correct and the key fob is pressed, your vehicle should start!


ctwistedpair (author)2014-01-29

Top notch! I've been looking for this forever. Gonna try this. Thanx for posting

Honzo (author)2013-12-29

Excellent project. I'd like to do the same thing but with the factory keyfob to unlock, lock, and pop the trunk. A couple questions...

1.) What's the current draw like on this device? Can you leave it plugged in for a week straight without running the vehicle without discharging the battery to the point of no cranking?

2.) I was looking at this exact relay. What is the programmability like? Can you set it up to trigger specific relays from specific commands? I want to simply be able to simply text "unlock" to open the doors.

Tetragammatron (author)Honzo2013-12-29

1.) The current draw is around 50mAh when none of the relays are engaged. Even for small car batteries, this means it can run for at least two weeks if not longer. I have a small quarter ton truck that I use this in, and I have left it for 2 weeks before and had no issues.

2.) This device (purchased on or ebay) comes with Android and iPhone apps so you can just press a button very easily to control the device. Alternatively, you can send a specific SMS to the device to engage one relay, but it takes the form of:


There are more advanced units that have better control of the relays in that you can send it an SMS to activate a specific relay, but you can also specify how long you want that relay to be engaged for. This unit does not have that ability; the timer only applies when you call the device.

Jayceevi (author)2017-07-29

My remote requires to press and hold 2x with 1 second each press.

Is there a setting to simulate on this gsm relay? I'm excited to start this project.

VictorD56 (author)2017-02-12


First, thank you for your generosity in posting this great Instructable. I have a Dronemobile in my wifes M3 and it cost me over $800.00 to have done. My Dodge Dakota has a remote starter that is kaput and I'm not going to fix it as it was put in the truck in 2002, so it's gone. I wanted to have a regular remote starter put in my truck and then do your instructable, or at least hope I can do it. I'm great at soldering, and wiring but this is beyond my usual schmoozual thing.

I have a couple of questions before I invest in parts. One, the GSM thing, do I have cell service to the phone that operates it? And if so, does AT&T have GSM or are they on another system? It's now February 12, 2017, so I want to make sure this still works there.

Someone asked about locking the doors and such, and I really need to do that. Also, in the pro installation of the Dronemobile, it has a system where you have to put the key in, turn it to on and step on the brake to make it work, otherwise the engine stops. Obviously, this is to keep someone from stealing your running (and toasty warm) car. Is there some type of thing like this built into your system.

Thank you so much for any help you can offer and thanks for being such a good person.



Bsw1985 (author)2016-11-20

Where do you get the SIM card for the phone? I don't want a monthly fee if possible.

yazenaswad (author)2016-07-25

How to program the 2nd relay through sms to go on for 4 seconds?

Thank you

ranjeevm (author)yazenaswad2016-09-23

See my comment below.

MAT01 (author)2016-08-06

Can this start my Hyundai without going thru Hyundai's internet which very expensive service at $400 a year. My mistake was I thought I had a remote that I could use like other similar remoted on key fob or via internet. I did not know I could only use it if I went thru Hyundai.

yazenaswad (author)2016-07-02

Thank you very much for the instructions, I am going to do it for sure. I have two questions if I may ask, I have three buttons on my FOB, remote start, lock and unlock. Can I wire the lock and unlock buttons to relay 2 and relay 3, so I can lock and unlock the doors? Do I need to wire relay 4 to the remote start button as well as the first relay if I wanted to use SMS command or call? will that work? Thank you once again

WilliamV31 (author)2016-04-12


KhanB (author)2015-08-10

pakhtoonistan radio

ranjeevm made it! (author)2015-02-16

I felt encouraged by the text command : #PWD123456RLY02=1 that kept the relay 2 on for about 1 minute. I added an electronic circuit to make relays 2 to 7 pulse (for 0-3 seconds) instead of toggling. Using this circuit I was able to activate all the functions available on my FOB! Isn't that cool?!!

The uploaded schematic provides all details to get the GSM relay to the next level. Note that OUT2 to OUT7 are the relay contacts (exactly as mentioned in the user manual of the GSM relay). Corresponding to each of these the circuit produces a pulse of 0-3 seconds (the duration can be controlled by turning the variable resistors VR1 to VR 6 in the schematic). A variable pulse can enable practically all functions on FOBs that utilizes the HCS300 controller chip. It is possible to use the circuit with little to no changes with FOBs that use other controller chips. Let me know if you need any help there - you will have to open your FOB and pass on the part number on the chip to me.

Another find during my exploration was that HCS300 does not need exactly 3V to function. It is therefore OK to feed up to 6.3V to your FOB should you decide to replace the battery with a voltage regulator. I would recommend that you utilize the LM78L05 voltage regulator for this purpose.

The circuit is centered around CD 40106BM, hex Schmitt trigger NOT gate, labelled U1. I prefer the BM suffix over BC because I suspect that M stands for military grade due to which the circuit can work in higher and lower temperatures than BC which would be commercial and so a little bit compromised in operating range (though the data sheets do not specify this).

I have sown the connections between my circuit and the FOB as dotted lined examples. The reason is because it is possible to connect both parts in a verity of ways based on your FOB model. For example some FOBs utilize diodes to activate multiple inputs on HCS300 to realize extra features.

To begin with rig up just one NOT gate on U1 and test it out before you assemble the full circuit. This way you can determine the approximate value of VR1 to VR6 and replace them with a simple resistor - this will reduce your efforts and will be considerably less messier.

It is important to connect all unused input terminals on U1 to either Vcc or Gnd with a 1M resistor. CD 40106BM/BE is a CMOS chip and all precautions related to anti-static handling should be observed especially during the winter months. Do not panic even if you blow the chip up I got 100 pcs for $10 on eBay / Aliexpress. (If you live in Toronto I can sell one to you for $1 and even make a decent profit!!).

For testing purpose you can also connect a 4.7K resistor in series with an LED between the output terminals of U1. You can even keep them on permanently if you like.

I used 4.7uF tantalum capacitors for timing purpose since I do not trust the electrolytic ones coming out of some of the countries. Tantalum capacitors will remain stable at high temperatures for a long time.

Remember that this circuit needs to work in a car and withstand shocks and jolts repeatedly. Use good quality solder wire - Radioshack does carry good quality solder so grab a handful while they are still around (feel sorry for them and us too!). If available use glass epoxy PCB to rig this circuit up.

Lastly if this works for you, do leave me a note. It takes hours to do something like this and it will be nice to know if you found it useful.

ranjeevm (author)2015-02-15

For those holding off this project for the price. I got one for $59 on ebay from a local Toronto seller. AliExpress has one for $72:

bhermance (author)2014-04-02

good one!

buxxy (author)2013-02-11

so cool. i'm currently awaiting arrival of this GSM relay purchased from ebay (
My AutoStart car starter has a range of about 30'. Soon i'll be able to start my car from the other side of the world!! lol

thakur900 (author)2011-03-08

I was thinking that would it not be possible to use this gsm relay for home automation? that would be really cool! can u give some suggestions??

Tetragammatron (author)thakur9002011-03-08

Yes, you can use it for home automation quite easily! I have a friend who has his wired to his thermostat in his cabin. He visits about once a month, so he keeps the place very cool. When he leaves the city to drive to his cabin, he text messages the device to turn on, and it activates the furnace, warming the house up for him for when he arrives so he doesn't have to wait around while the place warms up. The unit texts back confirming the state that the relay has entered (on or off) so that there are no mix ups.

Same goes for a water heater (wired into the control box of the tank).

I'm planning on installing an RFID activated electronically controlled door to my home, and I'll likely add one of these so I can remotely open the door if someone needs to get into my house, or I don't have my RFID tag with me. Since it has a white list of phone numbers that are allowed, it would be secure. Another use would be for a garage door or gate opener.

The one I used above can only be powered by 12V DC, but there are units that can be powered by 110V AC or 220/240V AC as well. These ones also have inputs so they text message you when the inputs get grounded. You could use this as a sort of alarm system, or could attach it to some kind of sensor (door sensor, infrared sensor, etc):

triscuits (author)2010-12-07

Wouldn't you need a voltage regulator on the key fob itself to prevent a surge of current or voltage from the vehicles battery? The voltage can range wildly depending on whether the truck is running or not.

Tetragammatron (author)triscuits2010-12-07

The battery is a 12V 23A battery, so the current shouldn't be an issue from the battery. The voltage was a concern. I checked with a multimeter on my truck and it ranged from as low as 8V up to 15V.

A voltage regulator is a good idea (its the proper way) but I was a bit lazy and didn't bother. I've been using it for over a year and have had no problems, but tossing in something to regulate the voltage to 12 volts would be a nice addition.

About This Instructable




More by Tetragammatron:How to start your car from a cell phone via GSM relay!
Add instructable to: