The short answer
ScoopFree crystal boxes run on disposable crystal trays, which PetSafe says last up to a month for one cat. To cut costs, reusable trays from PetSafe, Yangbaga or COSPARX let you refill crystals yourself, and liners protect trays for longer.
Disposable trays
Reusable trays
- PetSafe reusable tray with a bag of crystals.
- Yangbaga stainless and COSPARX stainless trays; COSPARX notes it doesn't fit every model.
Liners and crystals
Liners for ScoopFree add a cardboard insert against the rake. Refill reusable trays with ScoopFree crystals.
Products mentioned

Crystal self-cleaning litter box · PetSafe
PetSafe ScoopFree Crystal Smart
Wi-Fi, crystal trays.

Litter tray refill · PetSafe
PetSafe ScoopFree Reusable Tray with Crystal Litter
Reusable, fits ScoopFree.

Litter tray refill · PetSafe
PetSafe ScoopFree Sensitive Crystal Trays (3-Pack)
Unscented 3-pack.
Questions readers ask
How long does a ScoopFree tray last?
Up to a month for one cat, per PetSafe.
Can I reuse ScoopFree trays?
Use a reusable tray designed for ScoopFree and refill it with crystals.