There are various types of locking dog doors such as magnetic, automatic, and electronic. A locking dog door that is installed in an existing door would not require any extra locking devices. The lock on the door would be a source of security in itself. The dog is not going to care if the door is locked or unlocked. The dog just wants to be able to go in and out when the notion is there. The dog door gives that freedom to pet and also secures the house from potential intruders.

Good locking dog doors will provide an outlet to the outside world and be a strong defense against other animals trying to get into the home, of course, the dog will also be prevention. Your pet will be a lot happier and less likely to be destructive if they can go outside when they become bored or just need to do their thing. Working all day and then having to come home and clean up a mess is not the finish you want to have at the end of your work day.

I guess if you summed it all up, a good locking dog door would be convenient for the pet and less taxing on the pet owner. It would provide a necessity for the animal that is left home all day or night and provide the pet owner with a sense of security knowing their doors are locked in their absence. It is also a way for the dog to get some exercise when left home alone and less likely to be destructive due to boredom.