Gopro activated by movement, the ultrasonic sensor move the servo when something appears close to the sensor, it can be programed to take pictures or video, and also it can be programed to stop taking pictures when there is no movement in the sensor.
Advantages over normal infrared motion sensors a.k.a. PIR, is that it can sense reptiles and insects, it can also log the distance of the object, and it haves a range of 4 meters.
Step 1: Get the Parts
1 Gopro or any other camera
1 Ultrasonic Motion Sensor HC-SR04
1 100uF/25V capacitor
lots of rubberbands