Tell them you took it down to change the battery cause it was acting up. Life safety comes first. If its a hardwired smoke detector in an apartment building thats connected to the alarm panel then yes. It would automatically call the fire alarm company who in turn would call the fire department. You should be able to get out of a fine if you told them you were trying to change the battery and didn't know any better.
In addition to what the first answer mentioned, I can add, simply speaking, that a black hole has an area surrounding it called the event horizon. Its like the point of no return. All matter that passes or get beyond this line, it will suck by the black hole eventually adding to its mass. Black holes can't be observed because their gravitational pull is so strong that even light is absorbed by them and thus not reflected back. We know about their existence from calculations and from the lined of heated gas that is left behind an object being suck and spiraling inwards towards the black hole.