emacs-lock-default-locking-mode is a variable defined in `emacs-lock.el'.
Its value is

Default locking mode of Emacs-Locked buffers.

Its value is used as the default for `emacs-lock-mode' (which
see) the first time that Emacs Lock mode is turned on in a buffer
without passing an explicit locking mode.

Possible values are:
exit -- Emacs cannot exit while the buffer is locked
kill -- the buffer cannot be killed, but Emacs can exit as usual
all -- the buffer is locked against both actions
nil -- the buffer is not locked

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.