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This ordinary ladder has safety features to warn when it may be about to fall. It rings and flashes when it is standing at too acute or too obtuse an angle or when one of its ends starts to glide in relation to the building/ground. It also sounds when the pressure of the upper edge against its support
lightens (risk of falling backwards).
The warning system is only activated when there is weight on one of the rungs.
US patent 6,657,547
Sensing and warning system for ladder load [xaviergisz, May 15 2005]
||Fallen off a ladder recently [FJ]?