After reaching to work I left my car headlights setting in Auto and the battery drained by evening when I left work.
I guess auto is there for automatic on/off what did I do wrong. One thing I remember is when I pressed the lock button, I heard 3 short beeps.

This is my third day with this car.

 

I can tell you that leaving your headlights in auto should not drain your battery. The 3 beeps tells me that something else was on or open, etc. Did the door actually lock? I know on my 2012 if I leave the key in the car or don't something it will do a similar beep (although not lock the door). Even if you left the headlights in the on position they would have turned off on their own when you locked the car.

 

I know thats what weird, I guess now I need to repeat the issue again and try to find out whats wrong.

 

I think it's because you didn't turn off the power completely. Probably your car was in accessory mode. For the headlight, if you set it in Auto, it will turn off after a certain time (15/30 seconds) depends on your headlight settings.

 

This is really strange. Any update?

 

I did something similar once in a Cadi STS rental, I was using the radio after turning off the car, and then I left. The car stayed on in accessary mode. Without a turn-key, I didn’t even think about having to turn the car off. I suspect the OP did something similar. I actually almost did it in my TL once too, but then I remembered. Honestly, without a turn-key, it’s easy to do.

 

not sure what could have caused that but i do have a suggestion for the future. there is a setting in the MID where the lights will shut off as soon as you close the driver door. this is nice for two reasons, it wont drain your battery if you forget to lock the car and the HIDs wont flash when you lock the car, which will help them last longer.

 

Yesterday I tried to reproduce the similar sounds (when you press the clock button on the door - tech pkg, 3 beeps sort of thing). When the car electronics are in On position not the engine and if you try to lock the car it give this distinct sound.
Since it was my second day I did not pay much attention and walked away. Now I know if you leave your car in such state for long hours then the battery would die. Now if I do not hear the distinct locking sound then I wait and check if any other items are left on. Thats all the update.