Listening can end on a leave action people perform, or on stillness and timeout the system infers

What it is

Once listening is on, it has to be able to go off. Two families of off: explicit leave (another user-executable action or key) and automatic leave (the hand still long enough, the person walks out of frame, the session times out). They can coexist: explicit for people who want to go now, automatic for people who forgot. Automatic only: people think they have left and the system is still listening. Explicit only: they turn to pick up a cup and the command stream stays open on an empty room. This is not a single gesture's offset. That slices one command. This slices the whole listening session.

Why it happens

Explicit leave is the inverse edge of entry; the user initiates the flip, time is determinate. Automatic leave is inference on the system side: stillness may be thinking of the next command, walking out of frame may be fetching a remote, timeout may cut an adjustment that was not finished. Inference saves memory load and introduces false cuts. A sane structure is: explicit always available, automatic as a safety net, the net's clock and stillness threshold set by task risk. Tracking loss looks like stillness or leaving the frame, and will be eaten by automatic leave—that is a tracking-loss handling problem. Leave logic must not treat a dropped track as the user having gone.

Studying it

Four protocols: explicit only, stillness only, timeout only, explicit plus automatic. Interleave talking, turning to fetch, short pauses to think. Measure: cuts while people still wanted to listen, time still listened-to after they thought they had left, success of explicit leave. Wizard-of-Oz can let people key-leave first, to bound “leave when I want.” Do not measure leave on a pure command sequence; nobody there wants the session to end.

Where it stops holding

Taking a wearable off is already automatic leave in physics. A public terminal must auto-leave when the person walks away, or the next person inherits the session. Games may force leave on death or level-end. Stillness during a continuous drag is not leave; the timeout clock should pause. Automatic leave defined as “nobody in frame” will keep a session hanging on a pet or a bystander.

Applying it

• Always offer explicit leave. Automatic leave is a safety net, not the only means—unless the scene is a public device that must drop the moment someone walks away.
• Do not fire leave on a brief tracking loss. Pause the stillness clock during continuous manipulation.
• Accept with “go talk and come back” and “turn to pick up a cup”: what should continue is not cut; what should end can end.

Related

• Same group: C4.16.2 Timeout length trades unexpected cuts against timely release · C4.16.3 Warn before an automatic timeout so people are not caught mid-move · C4.16.4 Explicit leave should be symmetric with entry, for memory
• Adjacent: C4.15 Conditions for entering engagement · C4.02 The Midas touch problem
• Search: disengagement · clutch out · session timeout