Having previously gone from a HTC device that had a rotating actuator in the vibration motor to a Nexus that had a linear actuator , I can tell the M9 has a linear actuator. Rotating actuators vibrate more violently, so when placed on a flat, hard surface, you can more easily hear the vibration. However, it is said that although a linear actuator shakes less, it's intensity is greater and can be felt in the pocket better. Personally, I have found this to be true. I'm not sure why the manufacturers are switching motors, but I have a feeling the fact that motors with linear actuators consume less power has a lot to do with it. I find the vibration with my M9 to be good. It is comparable to my Nexus, but in comparison to previous devices I had that had rotating actuators, on the surface it feels weak.
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