“My son is playing games upstairs behind his computer. When we need him to come, we shout upstairs. This problem can be solved, I thought. I had several ESP8266 modules in house, and this was a project I could use them. I first made a test on my desk. Where I tried to let the ESP’s talk to each other. When that worked I added an annoying sound. To prevent my son from ignoring the message. There are several messages to send. The sender get a delivered message, so we can see if the message is arrived. When my son disables the annoying beep, the sender module gets a message. This message tells us that my son has turned off the sound. Which means that he is on his way downstairs. I intended to use two LCD 1602 displays. Somehow I was not able to get the second ESP8266 module control the display using I2C. Changing each component with the other ESP8266 module learned me that all devices were working fine. But not in this config. So for the receiver I attached an I2C Oled display. This did work as expected. After that I made two different housing to put the hardware in. The tiny Oled display is fragile. So I placed a transparent cover before the front of the housing. Both housing were drawn in SolidWorks, and cut on a laser cutter.”