LitterHopper - Automatic Refill System for Litter-Robot 4 Note: Not compatible with the Litter-Robot 3 or earlier models! The LitterHopper is your smart assistant for keeping your cat's litter box at the perfect level - automatically. This auto-refill system dispenses fresh litter into your Litter-Robot 4 when needed, giving your cat the best experience and saving you time and effort. Fully automatic litter refills The LitterHopper uses OmniSense sensors to detect when the litter falls below the MAX fill line and automatically dispenses litter during the next cleaning cycle. Always the right amount - even when you're away. Large capacity: 13 cups of litter The Hopper holds up to 13 cups (approx. 17 lbs of clumping clay litter), providing multiple days of use without needing to refill manually. Includes a new bonnet The LitterHopper comes with a new bonnet specifically designed to support the automatic refill function with Litter-Robot 4. Bluetooth & app integration Connect the LitterHopper to the Whisker app to receive low-litter alerts, firmware updates, and view the refill history. Stay in control with smart notifications. Easy installation No tools needed. Step-by-step instructions and a clear installation video are included for a smooth setup process. Compatible with various litter types Works with clumping clay litter and other light granules (such as crystals) that pass through the Litter-Robot 4's sifting system. Not suitable for wood pellets or biodegradable litter. Smart fill level calibration When activated, the current litter level is set as the optimal fill height. The Hopper will only refill when the level drops below this point. Efficient & intelligent dispensing Dispenses litter for up to 20 seconds per cycle and pauses when the globe rotates. If the level is still low, it continues during the next cycle. Built for any indoor environment Designed to function in a variety of indoor conditions. Keep the unit dry and clean for best performance and reliability.