0fraganator 10 years ago A passive infrared sensor like this one will work in detecting motion. When motion is detected by the sensor, it will set its output pin low. The simplest way to get your Processing application talking to the Arduino is with the Arduino Library for Processing. Simply load the Firmata sketch on to your Arduino and then setup processing for serial comms. The Processing application would configure the pin the PIR sensor is connected to on the Arduino to input, and then loop waiting for the input pin to read low. Once a low signal has been read, you can use Processing's video library to trigger an attached camera to take a photo or to start recording video.