Recent studies suggest that vibration of piano keys affect the perceived quality of the instrument, as well as the dynamic control and timing in piano playing. However, the time signals of piano key vibrations and its physical properties have not been analyzed and compared to the threshold of vibration sensation in a real-life playing situation yet. This study investigates piano key vibrations and explores the diversity of vibrations among different pianos with a laser Doppler vibrometer. A pianist was performing single keystrokes, note sequences, and a music piece excerpt on four concert grand pianos, five grand pianos, and two upright pianos. The measurements showed peak displacement levels up to 80 m and the frequency spectrum of the vibrations is dominated by frequencies lower than 500 Hz. Finally, a frequency weighting filter is introduced to show that vibration displacement time signals exceed the threshold of human vibration sensation for all evaluated instruments, when a note sequence is played in the bass to mid range with a single hand at forte level. The conducted experiments demonstrate that the vibration characteristics vary distinctively among the investigated pianos.