An accelerometer is a typical vibration sensor.
Vibration has a frequency and a magnitude, and typically contains several (or even many) superimposed vibrations. That is, it's not merely vibrating at a single frequency and magnitude, there's usually a number of them, all at the same time, piled on top of each other.
As a result, the output of the accelerometer usually goes into some sort of signal processing software to obtain the specific results that's wanted. A project of this sort is entirely doable but the airplane already has a decent vibration detector: the pilot. If something changes, the pilot ought to feel that.
The common approach to reducing vibration is by dynamically balancing the engine/prop combination. Do it once and it doesn't need to be done again until some component is changed. Usually a prop or engine overhaul will affect things enough that it needs to be redone.
There are excellent vibration test specifications available and labs that test devices for vibration. Sometimes, not always, a device intended for experimental aircraft will be tested, and if it meets the spec, the company includes that information in the specifications.
Dave
