It happens to me every now and then to drain my car's battery simply by leaving it overnight with some electrical device powered on.
Last time... pardon, second last time (about 2 years ago) it was an alarm beeping throughout the whole night. I was wondering what kind of an idiot ignores his car when its alarm goes bananas - well, it was me, as I figured out in the morning.
But two days ago it must have been something else, because the car was silent all night. Most likely one of the internal lights or so.
Anyway, in the morning I discovered that the remote wasn't working and I was unable to open any door but the driver's one. Fortunately I wasn't in a hurry so I simply rang my neighbor for help.
He drives a modern type of Renault. "Modern" means packed with lots of features like the "Start" button (an idea apparently stolen from the IT world) or most of the mechanical gauges being replaced by nice LED displays. Unfortunately, the battery in his modern car has been mounted in such an inconvenient way that both electrodes were barely reachable from the outside. It took us some 15 minutes (and plenty of words not existing in any publicly available dictionary) to connect the jump leads to both batteries. Then, with the help of a brief prayer to all gods of motorization, I turned my key.
And... nothing happened.
It took us another 10 minutes to find out that the jump leads were broken. Fortunately we had another set handy and - finally - the engine went off with a soft purr.
A great sound.