I've been following this thread with interest, then today had a similar issue, but thankfully without being locked out of the car.
The poor old Rover has been sitting quietly under the car port for a few weeks due to a combination of the poor weather and having no where to go. Today, I decided to give her a quick dust off and opened the boot to get some of my detailing gear. So far so good. When I tried to lock the car though, nothing happened at all. I gave a couple of extra presses on the fob, and was greeted by a ticking sound from under the bonnet, at the rate of around 2 per second (sound familiar?).
I disconnected the battery, and put it on charge. Then, after an hour or so, I put the battery back just to see if the ticking noise had stopped. It had, but was replaced by the alarm sounding instead
(made me jump a little!). A quick press of the unlock button on the fob silenced the alarm, so I'm guessing the ticking noise was the car attempting to trigger the alarm but with insufficient battery power to do so.
Battery is now off the car for a good long charge, which will hopefully sort the issue.
Hope this helps a little,
Cliff