If you are looking at having a dog door, then please consider the security aspects as the opening can be big enough for a small person to fit through. Pet friendly burglar alarm sensors are available which will not be triggered by pets up to a certain size. If you have concerns, then you may need to talk to a security professional. You may also need to talk with your insurance company to see how this may affect your insurance cover or premium.
Dog doors come in a variety of shapes and styles, although mainly in just two colours, white or brown, although there are a few exceptions. They are generally manual in type, apart from the Sureflap microchip pet door for small dogs only. There are exceptions to this, but either I don't recommend them or they are very expensive (petWalk). In addition to the basic feature of some form of manual locking, several dog doors have an additional slide-in closing panel. The manual locking is generally operated via sliding or rotating catches providing two way locking (free access or locked), or four way locking (free access, in-only, out-only, locked).
Manual Dog Doors
Essentially, most dog doors that I fit are manually operated, as I do not recommend the use of any that require the use of any collar attachments. The only exception is for small dogs only
Pros: cheap, no batteries, simple manual controls
Cons: any other cat, dog or suitably sized animal may use it. The larger ones may provide a security risk. The lock has to be manually operated as required
For further details see the Manual Dog Doors page
Microchip Dog Doors
I only recommend and use products from the Sureflap range, which limits the use of a microchip dog flap to small dogs only. There are larger models by petWalk, but these are very expensive and I do not install them, although my colleague at Four Paws Doors does
Pros: controls entry by reading your dog’s unique microchip implant (up to 32 pets at any one time). The standard model has a ‘curfew mode’, which locks and unlocks the door at specified times of the day. Alternatively the lock can be electronically switched. The latest model is phone app controlled and can operate the pet door remotely
Cons: Metal skins or foils in doors affects the microchip reader, requiring specialised fitting. The one (general retail) model available is for small dogs only
For further details see the Microchip Dog Doors page