If you haven't installed a pet door yet, you might ask your neighbors if they have a pet door and what problems they have. Of specific concern is if you have raccoons, possums, or other varmints that may want to get in. If you have an active watchdog, this may be enough to keep them at bay. If you have a small dog or cat, you'll want to keep these pests outside!
To do this, you'll need an electronic locking door. Most of the locking doors we've seen only prevent a stray dog or cat from coming in. They allow your inside pet to always go out, even if the locking system is off or the battery is dead. While this seems like it would be enough, raccoons are smart and can easily lift the door from the outside and crawl in – something a stray cat or dog can't do.
There is a solution – a fully automatic door that physically locks when closed. Unfortunately, these doors, while very good, are also quite expensive. See our review on the Power Pet door for one product that really does keep the varmints out!