general solution... emphasize that an action happened, communicate in other channels when users may not notice audio or visual cues, and reinforce virtual or simulated experiences...
These vibrations are generally propagated through the entire device, but can be localized, or placed only in specific components, such as the pen in a Pen Input device.
Most vibration is very coarse, and accomplished by a simple off-center weighted motor. Control is only by intensity and switching the motor on and off. Transducer-based vibration is also available, using tools typically employed for audio output to make more nuanced vibrations. This may simply involve the bone conduction transducer (BCT) included for use of hearing impaired users being re-purposed for general Haptic Output. Use of the BCT for audio output is not part of this pattern, and is beyond the scope of this book.
In addition, the device speaker can generate tones that vibrate more than they are emitted as audio, and thereby fall more into the Haptic Output range than that of Tones despite the output device being used.
Additional methods of haptic output are being developed in the laboratory, and may appear in production soon. These include the ability to sense objects that are not physically present, enabling tactile virtual keyboards for example.
Vibration responses and reminders. Two different things. Related.
TWO OR THREE???
Emphasis - hit a key, it confirms by buzzing or clicking
Response - delay... you do something and it vibrates to say "okay"
Notification - out-of-context alerts, vibrate helps you detect it when sound is off or muffled, and to localize when in a pocket, etc.
Haptic Output for Notifications (to include ring tones) is generally considered to be contiguous with the volume control system. Vibrate is either the setting between off and the lowest level, or can be enabled as a switch so it is on (or off) at all volume levels. While being used, vibration will be silenced in the same manner and at the same moment as Tones or Voice Notifications are. The same mute, cancel or silence functions will be presented when only vibration is enabled, and there is no audio output.
Vibrate isn't fixed, but should mean something, feel like a click when a click, feel harsh when "bad" feel soothing when "good" etc.
like sound... mean something... preferably emulate real items, such as key clicks or the texture of the item being dragged across...
Vibration and sound are closely coupled behaviors and can influence each other in undesirable ways. When both are needed, they generally must be alternating to avoid conflicting with or modifying each other. Alerts, for example, generally vibrate briefly, then sound a brief Tone, and repeat this until the notification alert time expires or the user cancels or mutes the output.
Do not over-use haptic output without a good understanding of the device hardware. If traditional motor-driven vibration is used, it may consume the battery excessively quickly.