Easy. First, the flaching light on the radio has nothing to do with the security system. That is just a warning for thieves that the radio will not work when removed.
The flashing light on top of the dash (centered) next to the window is a clue that you have a security system. This only blinks if the car is locked. If you raise the hood, you will notice a small security horn mounted at the top of the firewall centered between the windshield wipers.
You do not need a key fob to activate/deactive the security system, your key works just as well. My key fob no longer works (the service manager says the module in the car is bad and would have to be replaced and cost mega bucks), but I find using the key is just as effective as using the key fob and creates less bulk in my pocket.
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