A circuit breaker includes an accessory pocket, an accessory cover and a locking device to lock the circuit breaker such that an unauthorized switching of the circuit breaker from OFF to ON or from ON to OFF states is prevented. The locking device includes a first subassembly including a pocket housing. The first subassembly is configured to be installed in the accessory pocket. The locking device further includes a second subassembly including a cylinder lock. The second subassembly is configured to be mounted to the accessory cover. The first subassembly and the second subassembly are configured to self align upon final assembly of the circuit breaker to perform a locking function of the circuit breaker. In this way, the locking device prevents circumvention of a locking feature and selectively provides an ability to lock in an ON state of the circuit breaker.