It may happen, that an ECA model contains instructions, that may break your site. As ECA tries catching all the known risks automatically, this shouldn't happen really, but you never know. However, should you find yourself in such a situation, it's not too easy to get yourself out of it again. The UI may not be accessible any longer and disabling a model with e.g. drush won't work either then, because that bootstraps the Drupal site as well before it could change the config.
Only for situations like that, ECA provides an easy kill-switch:
Put this into your
settings.php somewhere and ECA will be completely disabled. Users with the permission
administer eca will be notified with a message on the screen, to make them aware that ECA is actually not working.
In this disabled mode you can fix the model, that's causing the issue by either editing that model or you can disable or delete that model. When done, remove that line from your settings again and ECA will continue working right away.