Hi!
I want to expand an arduino device which meters anxiety(yes, it can be mesured). I will add trembling as a new parameter and that's why I will use either a vibration sensor or an accelerometer. Which one do you think is more suitable and why?
Thank you! 
Hi, welcome to the forum.
You mean such a mechanical vibration sensor ? A spring and a contact ?
Like this one : Fast Vibration Sensor Switch (Easy to trigger) : ID 1766 : $0.95 : Adafruit Industries, Unique & fun DIY electronics and kits
They are ment to detect an object just laying on a table (no contact), and someone taking it away (contact).
To measure trembling, you probably want to be able to detect the amount of acceleration. That means you have to measure it with an accelerometer.
Peter_n:
Hi, welcome to the forum.You mean such a mechanical vibration sensor ? A spring and a contact ?
Like this one : Fast Vibration Sensor Switch (Easy to trigger) : ID 1766 : Adafruit Industries, Unique & fun DIY electronics and kits
They are ment to detect an object just laying on a table (no contact), and someone taking it away (contact).To measure trembling, you probably want to be able to detect the amount of acceleration. That means you have to measure it with an accelerometer.
I actually mean a piezo element like this one
http://www.arduino.cc/en/Tutorial/Knock
Although after searching I also think an accelerometer is a better choise.
Thanks again!