Off-center cap-level magnetic float sewer alarm

Claim 1

An alarm unit for detecting blockage of a waste line for installation in a service opening of a trap, immediately adjacent a horizontal waste line connected to said trap, comprising a circular conventional cap member including a threaded periphery for connection to said service opening and having a horizontal top portion closing said service opening and a switch member mounted in an off-center bore in said top portion of said cap member, said switch member including a central rod containing a magnetically activated switch extending from the inner surface of said top portion and a float member circumferentially surrounding said central rod and slideably moveable on said central rod between a first position near said top portion and a second position away from said top portion and defined by a lower stop on said central rod, said float member including a permanent magnet for activating said magnetically activated switch to close said switch when said float member is in said first position and to open said switch when said float member is in said second position, said switch member being mounted to said bore by a portion of said central rod remote from said lower stop and including electrical leads extending from said central rod to the exterior side of said top portion, said threaded periphery being fabricated such that said cap member can be tightened in said service opening while said switch member in the off-center bore is oriented horizontally away from the inlet of the trap connected to the horizontal waste line, whereby when said alarm unit is mounted directly to the service opening of the trap adjacent the waste line with said switch member oriented away from said waste line, said switch member is activated in response to a blockage condition, but is not activated by normal flow in said waste line.