@Yveaux @hek in fact it has to be debounced for it vibrates on rising and falling so it is important to see. maybe the bling delay would do it simply but someoone may remove the led...
Also through trial and error here is the way to manage it:
// Setup the reed
pinMode(DIGITAL_INPUT_SENSOR,INPUT);
// Activate internal pull-up
digitalWrite(DIGITAL_INPUT_SENSOR,HIGH);
attachInterrupt(INTERRUPT, onPulse, FALLING);
you have to power the pin to get the signal when both sides are connected.