How a phone fakes the click of a button that does not exist

This is less a set of instructions about haptic feedback than an argument, and it is worth saying so at the start.

The motor is a weight thrown against a spring

Inside most phones sits a linear resonant actuator, a small mass suspended on springs between magnetic coils that shove it back and forth. The coil drives that mass along a single axis, and the whole assembly is tuned to one resonant frequency where it moves most efficiently. Because the mass is accelerating, the body of the phone must accelerate the other way, and your fingers read that reaction as a tap.

Nothing on the surface of the device has moved relative to anything else, which is why the illusion survives underneath a sheet of glass. The actuator occupies real volume next to the battery, so its size is negotiated against runtime like every other component in the case.

Timing decides whether it feels mechanical

A real switch collapses within a few milliseconds, so a haptic pulse that lags your touch by much longer reads as a separate event. Designers therefore fire the pulse from the touch controller path rather than waiting for the application to finish deciding what the touch meant. The waveform matters as much as the delay, because a sharp attack followed by fast damping feels like a click rather than a hum.

Resonant actuators keep ringing after the drive signal stops, so the driver sends a short reversed pulse to brake the moving mass deliberately. Without that braking pulse the tap smears into a buzz, which is the clearest single difference between careless and careful haptic design.

Two motor types with very different manners

The older design is an eccentric rotating mass, a tiny off-centre weight on a motor shaft that shakes the whole body as it spins. A rotating mass has to spin up and slow down, so it cannot start or stop inside the few milliseconds that a convincing click requires.

Mechanically, it also vibrates in every direction at once, which is why older phones announced a notification with an undirected rattle across the desk. Linear actuators start and stop quickly because they only move a weight a fraction of a millimetre along one carefully chosen line. The trade is cost and volume, so rotating masses survive in cheaper devices, controllers and anything where a crude alert is sufficient.

Your finger localises a sensation that has no location

The actuator shakes the entire chassis, yet the sensation appears to come from whichever part of the screen your finger happens to be touching. Touch localisation is inferred by the brain from where pressure and vibration are being received, not from where the vibration was generated.

Under load, that is why one motor can appear to serve a whole keyboard of separate keys spread across the surface of the display. The illusion breaks when the phone lies on a hard table, because the surface conducts the vibration outward to your other hand.

It also weakens inside a thick case, which inserts damping material between the chassis and the fingers that are meant to feel it.

Haptics cost energy, so the system rations them

Driving a physical mass takes far more power than lighting a few pixels, so haptics are among the first things a low battery mode reduces. Systems also suppress repeated pulses during fast typing, because firing on every keystroke would leave the actuator ringing more or less continuously.

At the protocol level, operating systems expose a small vocabulary of standard effects rather than raw waveforms, partly to stop applications draining the cell unnoticed. That shared vocabulary is why unrelated applications produce the same handful of taps, thuds and stutters on any given device. Switching system haptics off recovers a small amount of runtime generally, and a noticeable amount for anyone who types all day.

Figures here are typical rather than guaranteed — check the spec sheet for your part.

What the illusion still cannot do

A click is easy because it is a single transient, while texture demands continuous changes in force under a finger that keeps moving. Producing texture needs either electrostatic friction across the glass or actuators that vary resistance, and neither is common in ordinary handsets.

Current hardware also cannot push back, so a virtual button never resists your fingertip the way a spring-loaded switch physically does. Because that resistance is missing, haptics confirm an action after it has happened rather than guiding the finger before it commits. Anyone typing quickly on glass is relying on prediction and correction rather than feel, which is why the software keyboard works so hard.

The takeaway

The click is a weight braking on cue, and the braking is the part you actually feel.

The constraint is almost always physical, and marketing rarely mentions which one.