Tracking products using barcode in SAP EM

Hi EM gurus

My client is planning to implement bar code (not RFID) in their warehouse (in SAP WM) and would like to track the products using SAP EM. Can you guide me how an event is triggered in EM when a bar code is scanned either by client or by their business partners (like 3PLs, Carriers etc)? Please guide me the pre-requisites to achieve this.

Thanks

Ravi