It is very essential to keep the door of fridge closed all the time. The refrigerator will not work efficiently if the door is left open. To avoid such situations, this [[wysiwyg_imageupload::]]project presents an interesting circuit that will sound an alarm if the door is not properly closed This alarm circuit will not  buzz till the door is opened and closed between the predefined times but if it crosses the predefined time it will start buzzing. NAND Gate is created by applying NOT operation to an AND gate. Hence, the outputs of this gate are opposite to that of AND gate when the inputs are kept same. This simple circuit project is based around transistor, switches and NAND gates. In the standby mode, the switch is closed and the current flowing through R1 is grounded through the switch.