Of things to read up on.
- radio frequencies, ham radios
- 3V3 vs 5V voltage
- integrated circuit (IC, chip, microchip)
- microcontrollers (MC/UC) or microcontroller unit (MCU): eg. arduino
- system-on-chip (SoC): eg. rpi
- electronic circuits
- semiconductors
- other types of motion sensors
- PIR (passive infrared)
- what most motion sensors in the wild use