Can I use it without a headrest in the car?

This product is a full-back booster only and does not convert to backless.  It can be installed in a vehicle seat without a VEHICLE headrest as long as the booster seat back is in as full contact with the vehicle seat as possible.

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