My car just shuts off on its own.

I would like to help but first I need to know the year and make/model of the car. A bunch of things could make a car suddenly shut off. How do you know there is no spark? Just to make sure try spraying some starting fluid in the air intake (disconnect it at the air filter) you may get lucky. Next scan the car for codes or have someone do it, many times there are codes stored that clue you in on whats wrong. Are you sure the security system is not the cause? Usually if this is the case the car will start for a second or two then shut down (no spark). Try this: lock and close the door, then with your key unlock then lock the door five times (without opening the door) then open the door and try to start it. Let's start with these things. Remember, make, model and year?

Possible problem with the ignition switch. When it stalls, if all power goes dead (like when you park the vehicle and pull out the key) I would suspect the ignition switch. When they go bad, you usually can get the vehicle to start right back up for awhile till the next stall until, they just finally completely lose the connection. Hope this helps you. The fuel pump is possible as the issue if power remains on inside the vehicle during the stall (radio, heater, lights, etc.).

ALONG WITH MORE INFO ADD TROUBLE CODES IF ANY