> >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
They defeated the ultrasonic detector by simply holding a sheet (as in one
off your bed) in front of them, and walked at a normal pace. (Might have
been a blanket.) Not quite what you were thinking.
If you're think 'OMG that won't work', well, so did everyone else! OMG, it
does! Yes, I tried it.
One way they beat IR was to get behind a pane of glass (but I already knew
that one). BTW, that's new glass, some really old glass will pass IR.
Rather than walk around holding up a sheet of glass, they put a small piece
on a rod, and hung it over the detector. That was actually quite clever.
I recall a documentary once where the thieves beat the IR detectors in a
warehouse by building a wall of boxes (TVs fridges etc), like you said.
Once the wall was high enough they could do what they pleased behind it.
They knew the building layout though.
Where I once worked had an IR sensor that unlocked the door when you were
leaving (so you didn't have to press a button). I didn't have my pass one
day, so I slid a piece of metal that had been lying in the sun under the
door.
Cool doors, glass with electromagnets to hold them closed.
Tony