Another John wrote:
I've said this before in a similar thread a few months (a year?) ago:

- I paid about 800 for our electric, remote controlled roller door,
fitted by "a bloke who works at the factory where they make them".

- It's a cheap door, but we have been delighted with it (WONDERFUL
compared to the extremely heavy, draughty, up'n'over that it replaced.
However ...

- ... the only safety mechanism to prevent it relentlessly closing on an
obstruction is a 'magic eye'. This work fine for cars, people --
anything bulky; but if you have left (say) a spade propped in the
doorway, it won't see it. It will close, and it will snap its flimsy
plastic clamps, which secure it to the roller. It is a big and fairly
skilled job to replace these.

- Thanks to breaking the clamps TWICE, I have developed an intensely
ingrained habit of watching the door close. This habit is still not 100%
good enough -- I closed the door on a shallow box only last week --
missed by the magic eye, and also by my own eye: a horrible crunching
ensued, but I *think* I may have got away with it as Basil said.

- Next time I get such a door installed I will splash more money and get
one with e pressure detector across the whole bottom edge, which will
stop, and reverse, the mechanism as soon as anything is touched: that is
the proper way to do it (I now know :-( ).

John

Up and over motorised doors sense the closing force and reverse when a
current limit is exceeded. I don't know if roller doors have this function.