For some IoT applications, we use sensors as push button, reed relay (rain sensor uses reed relay), magnet security sensor for windows/doors (MUC sensor).. Usually the output pulse of this kind of sensors is very short and if we read the state of the sensor using board with digital or analog inputs, we can lost the pulse because we will read the state once per every one, two or more seconds. At this situation we can use Contact sensor board. The boards has a connector with two screw, with labels 0V..In, where we can connect the contact sensor (the monitoring normal open contact). When the contact is closed for short time, the output of the board Out will become to a high level for time between 1 and 8 sec, depends on potentiometer, which is located on the board.
The other connector with three screws is for power supply of the board: 0V, +5V and the middle screw Out is an output signal of the board.