Wire brackets blocking circuit brakers from tripping
As Tyson pointed out modern breakers are "Trip Free" meaning they can trip even if their handles are locked on.

The "wire bracket" you refer to is a breaker handle lock that is used just to keep people from inadvertently turning a breaker on or off that you want to stay off or on.

I put one on my sump pump circuit. There should also be one on your smoke detector circuit.