How would they get in and find the fire and turn it off. With all the lights off and all the doors locked?
I didn't check into the background history of 'peeing on a fire hydrant' but it was probably one cheeky Dog that started the trend.
Just grab hold of the unit and turn like you are trying to unscrew it. When it releases from the base, there will be a wite in the back of it; usually with black , white and orange wires. Just unplug the unit and toss it. Remember to take out the 9 volt back up battery if it's still good. To replace it with the new on, either plug the existing wires into the new one ( if it's the same type ). OR, remove the existing plug from the wires by unscrewing the wire nuts ( wire splice caps ) . MAtch the wire to color. The orange goes to the RED house wire. Careful of the black and the white. You can get a shock from the black.Replace them one at a time and you won't have any problem.
