On the ops desk the pre-alert is what lets the destination agent start clearance and delivery planning while the cargo is still in transit; if it arrives late or incomplete, the shipment lands before anyone at destination is ready to act on it. The decision the term drives is when to send it and which documents to include, because the destination office can only work with what it actually holds. Forwarders also use the term for a second notification at destination: a branded pre-alert to the end consignee, prepared from the carrier's arrival notice, so the consignee can start clearance and arrange pickup. A pre-alert is not the same as an arrival notice: in either sense the pre-alert comes from a forwarder or its agent, while the arrival notice comes from the carrier or its destination office.
Glossary
Pre-alert
The document package an origin forwarder or agent sends to its destination counterpart before the cargo arrives, typically copies of the bill of lading or air waybill, the commercial invoice, and the packing list, so the destination office can prepare customs clearance and delivery.