We can't tell you how many times we've come home to find random cats we don't know hanging around our house, while our own cat is out doing whatever it is cats do. They waltz in through the cat flap and make themselves at home, even helping themselves to our cat's Whiskas.
That's why we're considering the SureFlap, a secure pet door that only opens for the pet or pets that have approved RFID chips implanted under their fur. Any other animals -- such as the evil gang that likes to get its fur all over our couch -- would be turned away. You don't have to have a special chip implanted, either -- it'll recognise the most common types of ID chips that record your pet's details in case they get lost.
This is a pretty high-tech solution for a low-tech problem, but if it's a situation you're in, it's a perfect answer. -Matt Hickey