Hi, I state that he never used arduino and that he has never had to deal with home automation ... so I apologize for the ignorance, I should buy a relay that is able to withstand the voltage to turn on a 'car! which relay I buy? many thanks in advance.
PS: I apologize for any errors, but I am using the translator 
What do you mean by "turn on a 'car!"?
We need to know what you are doing in order to give best advice.
Weedpharma
Thanks for the answer, my aim is to start the engine of the car with a remote control
If the car is recent it will take a lot more than a relay, probably at least two.
As electronics should be quite obsolete due to a microcar, obviously OCCE a relay to turn on the ignition and another for the engine it?
PS: what would be the model of relay to buy?
I think you're trying to say one relay for ignition, one for the starter. (the "START" position is a combination of the ignition ON + starter relay ON. (probably 30A or more)
Remember that modern cars need to see the RFID-transponder in the keyfob to allow the motor to start.
// Per.
The processor in the Arduino is not qualified for use in automotive products. The data sheet says:-
. Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications.
Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications.
That's an interesting footnote. I wonder why that is.
I wonder why that is
Because they haven't passed or tested for all the tests that an automotive qualified device has to pass.
It also covers there arses.
To echo something that has been stated before, to the OP, there are certain projects that we will not assist the execution of in any way.
Specifically where public safety is critically involved. The possibility of a car spontaneously starting, possibly without the gearshift and brake interlocks, or running in an enclosed garage, is sufficient cause to refuse to be involved.
unfortunately relay greater than 10A are impossible to find on the market! But I believe that the processor is not capable of dell'arduino domotizazioni advanced, not to a simple start ...
And a Happy New Year to you also. 
dandi98:
unfortunately relay greater than 10A are impossible to find on the market! But I believe that the processor is not capable of dell'arduino domotizazioni advanced, not to a simple start ...
Wrong on both counts.
WHY do you want to start a car by remote control ?
Why does the car engine need to be running with no driver in the vehicle ?
Go to the salvage yard and pull some relays from a junk car. Cheap and plentiful.
raschemmel:
WHY do you want to start a car by remote control ?Why does the car engine need to be running with no driver in the vehicle ?
Someone must want to since it is a pretty common feature on new cars. You don't live where it is cold, do you? 8^)
You don't live where it is cold, do you?
California. Here 38 degrees is cold.
I know, I was raised there and stayed over this Christmas. We delayed our trip back to NM due to the blizzard. At our house in NM I am the remote starter.
The last time I actually saw snow was on a trip to Aspen Colorodo.