Can I use it without the latch if my car doesn't have a latch system?

Yes.  It must be secured using a vehicle lap/shoulder belt, even when unoccupied.  It cannot be installed with lap belt only.

If you’d like to find out more about the Monterey 5iST FixSafe™ visit our store: https://store.diono.ca/monterey-5ist-fixsafe/