Channel Activity Detection (CAD) is a feature implemented within the LoRa chip itself that allows a node to determine, before transmitting, whether another transmission is currently in progress. To do this, the transceiver actively correlates the typical chirp patterns of a LoRa transmission and reports within fractions of a millisecond whether the channel is clear. If it detects activity, the node waits briefly instead of transmitting—a process generally referred to as Listen Before Talk (LBT).

Compared to evaluating the received signal strength (RSSI), CAD is significantly faster and more reliable because it does not have to wait for the receiver to lock onto a preamble. On SX126x and LR11xx chips, both the preamble and payload are detected; on SX127x chips, only the preamble is detected. However, interference that is not LoRa signals—such as Wi-Fi or other wireless services in the same band—is not detected.

In MeshCore, CAD has been available in the firmware branch since June 2026 dev and replaces the previous RSSI interference detection, which was considered unreliable (int.thresh). The feature is enabled via the CLI using set cad on or set cad off . It is enabled by default on Companions, but disabled by default on repeaters, room servers, and sensor nodes. The benefit is particularly noticeable with short messages and commands in dense networks. In highly exposed locations with a line of sight to many repeaters, however, the channel may be considered occupied almost constantly; in such cases, a four-second timeout applies, after which the message is transmitted regardless.