First, the driver's side door would not lock/unlock. Now all the door locks are completely dead, and the engine won't start. Can you guess what's going on?

Thanks for the suggestion, Stevieray1. I do not have access to a voltmeter, but the battery seemed fine last time I started the car (two days ago.)

your welcome

No lights, no horn. I'm suspicious that, because the car cannot be unlocked properly, everything is disabled and that this might not be diagnostic of a dead battery. Does that suspicion hold any water?

I don't understand you , do you mean , you have no lights , horn or locks , but you don't think the battery may be dead? What about brake lights? Engine 'won't start' does that mean it does 'turn-over' but will not run?--Tried jumping?

What I mean is that I suspect that the security system may be disabling everything. Will try jumping the battery tomorrow.