If you currently have more than one pet, or plan to have more pets in the future, additional considerations include:

* Size the door for the largest pet

* If using a electronic locking door, consider the expense of extra keys

* If the pets are very different in size, such as a large German shepard and a small cat, you might be wise to consider two doors.

* If some of the pets should be restricted on how they use the door, you may need two doors, or plan to not provide the restricted pet with a collar key.