How do I feed my Arduino and shields?

I will give the task of making a breathalyzer Car consisting of Arduino Mega and its respective sensor MQ-3 for blowing and detect alcohol, if a lot of alcohol is detected, it will send a signal to the relay so that it can not be start your car while a message to the cell of close to drunk people, this shield with SIM900 GSM is sent; if no alcohol is detected, the vehicle function properly.

I'm thinking of implementing a GPS module to send the coordinates in the message Could do the latter?

Well, my question is how do I feed all this in the car?, what do you recommend?, What you would use? or what have you used?

Any other advice for the project is more than welcome. Thanks in advance.

Well, my question is how do I feed all this in the car?

Are you asking how are you use a relay to prevent the ignition of a car, get data from the breathalizer, and use a GPS module.

Also can you clarify what you mean when you say...

while a message to the cell of close to drunk people

???

Do you want to send a text/SMS message to everyone who is near you while your drunk??

If so.. you can't because that would involve using the Arduino Yun and hacking into cellphone network companies.

Also you don't want other people to get a text message out of the blue saying the man/woman in the blue ford camaro is as drunk as a rock. That could cause accidents from laughter.

Anyway this project is one i've never heard before and it seems very interesting and i'm happy to help

Are you law enforcement? Are you wanting to sell this concept to law enforcement/government? Or, is this for the individual, that wants to not drive after to many pints?

Do you know anything about automobiles? The key switch connects power to all the stuff that energises the starter. If you have a relay in that ckt. that keeps it from connecting power, then the starter will not turn.

Sorry, I did not know me well explain. I meant to send an SMS to the family, for example their parents in case of a teenager. This product'm not going to give any government, in fact, already exists, but I'm going to put extras.

I just want to know how serious the best way to feed all this in the car.

If you understand not because I'm translating from Google, I do not know much English hehehe