I forgot to turn off the light in the hallway. He who doesn't have it in his head, has it in his legs. The solution to my problem. A smart light bulb. E27 denotes the cross-section of the bulb socket. The cross-section of the thread of the E27 bulb holder is 27 mm. Installation. Settings. Open the Play Store. Search for LSC Smart Connect. Not this time! My new app! Goodnight!.