Dear Simon,
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Its critical:
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There are some areas which are critical as human safety depends on them in many respects.

The lift system ( if it is the elevators that move up n down in tower buildings, you mean.) is very critical. Human life depends on the adequacy of every system employed in it.

The mechanical and electronics as well.

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Your querry:
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Now your question.

Its too vague and not clear as to what exactly you need.

There are many of different systems which can be in a lift.

I hope your question concerns only the elctronics involved.(Don't do mechanicals of the lift by yourself ever....if you are not a qualified designers for it)

Please elaborate your question.

For your information just today a contractor has asked me to make IR sensors modules that fit in lift doors.
It will be fun if both work in conjunction.

Babar/