Can a linked or web device send messages independently?¶

Often, yes. Once authorised, a desktop application, tablet or web session may send through the messaging account without someone handling the primary phone at that moment.

Independence depends on service design¶

Some services use the primary phone only to establish or approve the link. The additional endpoint can then communicate directly with the service. Others relay activity through the phone or require it to reconnect periodically. These arrangements can change between platforms and versions, so establish the relevant behaviour for the period in question.

Synchronisation can make the origin difficult to see. A message composed on a computer may later appear in the phone's conversation history as though the phone created it. Account-level content is not necessarily device-level proof.

Identify the active endpoint¶

Preserve the linked-device record, session identifier, link and last-active times, security alerts, browser storage and desktop application data. Compare those records with artefacts and connectivity on the primary phone. Shared systems, unattended browsers, remote access and compromise may affect who controlled the session.

Unless the originating endpoint is established, report that the account sent the message. The event alone does not prove the primary phone was present, handled or even online.