I passed a CAT 6 ethernet cable through the grommet and used drywall screws to sandwich the bracket, drywall, and a 2x4 in my attic together.
To fasten the motion sensor housing to the bracket, M3 bolts and nuts were used. 

This has been a part of an existing home security project, where these motion sensors are connected and controlled by a raspberry pi. Some basic code is included in the project files. This code plays a tone when a motion sensor is triggered. Use https://pinout.xyz/ for referring to the raspberry pi's pinout in order to connect the motion sensors. Power the sensor using a 12v power supply.

Please note that if using an ethernet cable to power this 12v motion sensor, pair the leads in such a way as not to overload the cable. This method is shown in one of the photos, using:

• 3 wires for +
• 3 wires for -
• 1 wire for the first relay terminal
• 1 wire for the second relay terminal