Yes, feral cats will use a cat door for the window. 

Creating a Cozy Haven: Installing a Window Insert Cat Door for Feral Cats

Winter's chill can be particularly harsh for our feral feline friends. After noticing a regular visitor in my backyard, I decided to create a safe entry point using the cat door window insert I had created for my stray to family feline named Nikki. 

The Installation Process: The beauty of window insert cat doors lies in their non-destructive nature. They fit snugly between the window sash and sill, requiring no permanent modifications. I chose a small, 2-way locking flap from Closer Pets.  This model for better insulation, ensuring my heating bills wouldn't skyrocket while providing warmth to my outdoor visitor.

Setting Up a Safe Space Inside: I designated a corner of my mud room as the "cat sanctuary." I placed a cozy bed made from an old sweater inside a covered box, creating a cave-like structure that appeals to feral cats' natural instincts. A small litter box and fresh water bowl completed the basic setup, positioned away from their sleeping area.

Acclimation Tips: Feral cats are naturally cautious, so patience is key. I started by placing food near the outdoor entrance of the cat door, gradually moving it closer to and eventually through the door. It took about two weeks before my visitor, now named Felix, figured out the cat door mechanism.

Safety Considerations: To ensure this setup remains safe for both human and feline residents:

• Install the cat door at a reasonable height that allows easy access but prevents other wildlife from entering
• Use a microchip-activated door if you're concerned about raccoons or other unwanted visitors
• Keep the indoor safe space separate from your main living area until the cat is vetted
• Place security cameras nearby to monitor who's using the entrance

The Reward: There's something incredibly fulfilling about watching a formerly hesitant feral cat confidently use their special entrance during harsh weather. While Shadow remains cautious, they now have a reliable shelter during storms and freezing temperatures.

Remember, while providing shelter is important, connecting with local TNR (Trap-Neuter-Return) programs is crucial for the long-term welfare of feral cats in your community.