Recently I was testing the Low cost SW-18020P Vibration Switch which I bought online from this website. I found it cool for basic vibration detection. This switch is not ultra precise like MEMS sensors but they do the work in most of the cases for non critical applications.
When I opened the plastic cover from the switch I saw that this switch is made up of a small spring mechanism, which makes the Switch ON when the applied vibration force is at above a certain threshold.
This switch is very low in cost and can be used in variety of vibration detection projects. It has to legs coming out of it. Normally the two terminal are insulated by a resistance value more than 10MOhm. When someone applies vibratory force on the switch, spring inside the switch vibrates and makes a momentary short circuit between the two terminals.
I made a simple LED circuit to verify the working of SW18020P Vibration sensors. I simple used Vibration Switch as an on-off switch. When vibration of above a threshold is present on the sensor, the LED glows while when there is no applied vibration LED does not glow.