Homebrew PCBs

>
>It was also interesting to see which tricks worked on the ultrasonic

You can read the specifications: they all are AC coupled with poor 
response at very low frequency.
slow movement

>and IR motion detectors,

slow movement or thermal isolation (can use a cardboard)

>  but none involved a PCB.

no, but everyone is interested in security


>If you think about it, carrying a RFID key, keycard, or even a simple
>barcode tag would be safer than a fingerprint lock.

right