that is why I said a LED wired directly to the device in question. not something controlled by a processor.
the camera needs power to run, if you wire the LED to the power lead of the camera it will light up when the camera gets power.
yes you can have the LED fail, or a bad solder joint, but other than that there really isn't much that can go wrong with this (and there is no way that this could fail in a way where it lights for the user using the camera, but not for the attacker.