Me Micro Switch is a physical switch. It sends a signal to the controller when it is triggered. It is perfect to use in conjunction with makeblock components.
The Me-Micro Switch should be used with Me-RJ25 Adapter. 
 
Features:
Small and easy to mount
Cable included, no soldering needed
Comes with Arduino library for easy programing
Acrylic bracket to attach these switches to makeblock components
 
Specification:
Rated voltage:250VAC
Rated current: 5A 
Switching Life: 1,000,000 cycles min
Dimension:Length:20mm Width:6mm Height:24mm
 
Part List:
1 x Micro Switch
2 x Self-drilling Screw M2x10
1x Micro Switch Bracket B
1 x Cable