A tactile detent (a sudden drop in resistance at the fire point) marks that the action was received

What it is

The pad travels down, resistance rises, then at some point collapses and the cap drops a notch—that event is a tactile detent (tactile point). It is treated as a mechanical receipt that the system has taken the press: no lamp, no wait for sound. Finding a key is about whether it is there and whose silhouette it is. The detent is a sudden break in this key’s travel. Whether that break coincides with electrical make is a later misalignment problem.

Why it happens

A rubber dome going over-center, a metal snap dome collapsing, a mechanical switch’s contact leaf passing a dead point: all put a peak-then-drop on the force–displacement curve. Meissner and Pacinian channels in the pad read that break as an event, rather than integrating the whole travel into “probably pressed.” People use the event to terminate the action: time to release, no need to watch for a highlight. A linear spring can finish the travel without a separable “fired” mark, so people either bottom out to be sure or release before make. A detent is confirmation in time, not a landmark in space: it says “this one is done,” not “you are on that key.”

Studying it

Plot the force–displacement curve, mark peak force, drop amplitude, and where the tactile point sits relative to end of travel, then collect human confirmation judgments.

Independent variables: presence of a drop, drop amplitude, peak force, whether vision and sound are allowed. Dependent measures: moment the person reports “pressed,” early-release rate, superfluous bottoming, missed actuation with eyes covered.

A peak on the curve is not the same as a usable event: a shallow drop is filtered by skin. Measure under repeated presses at the target force; do not stop at one engineer’s feel comment. Eyes-covered and gloved conditions are mandatory—the detent’s home ground is occupied vision.

Where it stops holding

Linear Hall keys and force touch deliberately omit a mechanical drop and confirm with sound or a motor; insisting on a detent there would reject a lawful design. Very light notebook-trackpad keys have a small absolute drop that children and gloves may miss. In vibration, a single over-center can be masked by chassis shake. A very sharp detent at a high actuation force confirms clearly and also cuts false hits, but slows fine repeats—that is a force trade, not a failed detent.

Applying it

• Keys that must count without looking need a drop the pad can read on the force curve; do not rely on an on-screen highlight alone.
• Put the cue to end the action on that event: the key may travel a little further to bottom, but confirmation should not require slamming the floor.
• Verify: block vision and sound, have people release when they think it has fired, and compare to electrical make. Frequent early releases or obligatory bottoming means the drop is not a receipt. Repeat in the product’s gloves and on the target vibration table.

Related

• Same group: C10.08.2 Keys with too little travel cannot give clear mechanical feedback at the moment of press · C10.08.3 If the detent and the electrical make point are out of sync, feel and effect misalign · C10.08.4 Thin devices often sacrifice travel and simulate a detent with a haptic actuator
• Adjacent: C10.01 Tactile Localization of Physical Keys · C6.02 Key Travel and Tactile Confirmation
• Search: tactile point · force-displacement curve · actuation confirmation