Review on 🏃 Highly Efficient DIYmall HC SR501 Motion Infrared Arduino for Enhanced Arduino Projects by Mike Goodwin

These modules are excellent for most applications for which they are intended. If you need a very tight movement (between 2 meters and 2 millimeters) you need sound sensors. I tested them with ESP-12 and got great results. For those who complain about false alarms and unreliable readings. If you switch a GPIO pin to input and hang a long cable from it, that cable can pick up noise and cause the voltage on the GPIO pin to change. This can trick the system into believing that the switch has changed. To fix this there are a few things you can do.1. Add pull-up resistor 2. Add shunt capacitor 3. Shield on wire 4. Use twisted pair. The pull-up resistor is a resistor between the GPIO pin and 3.3V. The exact value is not critical, a value of 4.7K is commonly used, as is 10K. This ensures that when opening of the switch the GPIO pin goes high. The bypass capacitor is a small capacitor (pF range) connected between GPIO and ground. This provides a path to earth for all radio signals received over the cable and does not confuse the system. Shielding or using twisted pair are other ways to reduce the effect of radio signals on the system.