Width of the edge hot zone versus false triggering

What it is

Too thin a band and an arc entering from the bezel misses, so the edge gesture becomes hard. Too wide and a tap on an edge button, or a horizontal page flip, is taken as an entrance. Width is a lever where hits fight false fires. No millimetre value is right for every screen and every hand.

Why it happens

When a thumb enters from the side, the first contact is often several millimetres inside the glass: the pad center is not the fingertip, and a side arc drops even farther in. The band must cover that bias, or “I clearly started at the edge” is refused. Meanwhile back arrows in a nav bar, avatars at the left of a row, and the current page of a full-width pager all live in the outer strip. Each millimetre of extra band is a millimetre of those objects’ downs being peeked at by the edge recognizer. Some systems delay capture—“give the app a short stretch, then steal if displacement is enough”—which eases the fight and makes the edge gesture meaty, or lets the app scroll a little and then yank it back.

Studying it

Vary band width (say 8, 16, 24, 32 mm equivalent) and mix tasks: edge entrance, tap an edge icon, flip a page sideways. Plot hit rate and false-fire rate against width and find the crossing. Split left/right hand and large/small screens. List “first point in the band but immediate lift” separately: that is either a tap on an edge control or a failed edge gesture, two different design outcomes.

Where it stops holding

A case hides the real glass edge; the user’s “edge” is the case edge, and the band in glass coordinates has shifted. In landscape the left and right edges shorten and the thumb arc reroutes; a portrait calibration does not apply. Games that park important buttons in the lower corners will misfire on any non-zero band; those apps often request exclusive edges.

Applying it

• Set the band in physical millimetres to cover thumb-entry bias, but do not cover the hit region of a primary edge button; the button beats the edge gesture.
• If overlap is unavoidable, delay capture: a short contact taps the button; a clear inward displacement becomes the edge gesture, and the button must roll back its pressed state when stolen.
• Measure real devices in their cases. Twenty entries from the case edge, twenty taps on an edge icon. Plot misses and false entrances together and tune width until both curves are acceptable, not until one is perfect.

Related

• Same group: C3.13.1 An edge swipe depends on the screen boundary as its starting feature · C3.13.3 Direct conflict between edge gestures and in-app horizontal scrolling · C3.13.4 Curved and bezel-less screens change the physics of the edge band
• Adjacent: C3.14 Back gestures · C2.02 Minimum touch target size
• Search: edge inset · false edge swipe · hot zone