The SubscribeCOV service lets a client subscribe to value changes of a Property of a remote Object: the device then automatically emits a ConfirmedCOVNotification or UnconfirmedCOVNotification on each change, avoiding the need to poll.

Change Of Value is a push mechanism, conceptually similar to the Send-on-Change behaviour of KNX Group Objects. Its benefits are substantial: drastic reduction of network traffic compared with cyclic polling, immediate reactivity (no polling delay), and the ability to scale to thousands of monitored points without saturating a controller. Two flavours exist: ConfirmedCOV with an application-layer acknowledgement (reliable but heavier) and UnconfirmedCOV without acknowledgement (best-effort, lighter). Subscriptions expire after a configured lifetime (typically hours) and must be renewed by the client.

Always confirm COV subscription renewal logic when commissioning: a supervisor that silently lets subscriptions expire produces a frozen-looking BMS with no obvious error message.