“I wanted to make a motion detector that would notify me every time my garage door is opened. I was playing with PIR sensor for a while but after having some setup issues (sensitivity x time) I decided to use the HC-SR04 sensor instead…and it works like a charm. The idea is simple: you setup the detector so when the door (or window - depends on how you want to use it) is opened, it gets in the way of the sensor so the measured distance is changed. The advantage using the UltraSonic sensor instead of PIR huge. It can’t be triggered with light or mosquitoes which was the main reason I didn’t want to use the PIR.
What you will need:
WeMos D1 mini board - eBay - USD 3.47 (other boards are possible - but be aware that e.g. NodeMCU ESP-12E V1.0 gives out only 3.3V and the HC-SR04 sensor needs 5V) HC-SR04+ Ultrasonic sensor - eBay - USD 1.06 Blynk app(if you are new to Blynk and using iOS device, you will need to borrow an Android phone for setting up the notifications) Breadboard or soldering ironWiresComputer with Arduino IDE installed”