Its a small IoT implementation using CloudMQTT, NodeMCU and ESP8266. The NodeMCU monitors the status of the door using an ultrasonic sensor and raises an alarm if the door is opened. Additionialy, the NodeMCU also sends the status of the door to theuser's smartphone using cloudMQTT with real time data.
For detailed explaination, visit Techquipped: https://youtu.be/tPXwLXKJ6d8