vibration alarm
In some mobile devices such as smartphones and cell phones, there is a vibration alarm in addition to the acoustic alarm by means of a ringtone. With the vibration alarm, the cell phone vibrates and the vibration is perceived by the cell phone user.
br> The vibration alarm has the advantage that the alarm is not perceived by other users than the cell phone user and no one feels bothered by it. Moreover, the vibration alarm is perceived haptically even in the presence of strong ambient noise, where an acoustic alarm can easily be overheard.
The vibration alarm is triggered by a mini-motor or by the built-in loudspeaker. The mini-motors are only a few millimeters small and have an unbalance. This imbalance is caused by a small weight that is not centered on the motor shaft. When a call comes in and the vibration alarm is turned on, the mini-motor rotates and starts to vibrate due to the imbalance.
If the speaker is used for the vibration alarm, it is driven with extremely low frequencies that cause the membrane to vibrate.