These features offer increased mounting and detection flexibility all while being as safe as a photoeye. When the beam is broken, the laser turns off and the ESP8266 requests a specific web page that will send the alarm message to your device and trigger the notification. Laser Beam Break Detector. 2. You'll need to make sure that your hub has back-up power and a way to send notifications even if the lights are out. Seco-Larm Enforcer Reflective Beam Sensor with Square Reflector, 35' SEE931S35RRQ. It's written for arduino, but everything applies to the NodeMCU, as well. You may need to add a transistor similar to the one for the laser in order for it to work.