Sewer back up warning system

In combination with an upstanding pipe section whose lower end portion is in communication with a liquid flow line and which pipe section is subject to an unwanted rise of liquid level therethrough from said flow line, and an alarm device including dielectric support means supported from the upper end portion of said pipe, first and second laterally spaced apart and depending elongated electrically conductive support members having their upper end portions mounted from said support means, an elongated float arm having one end pivotally supported from the lower end portion of said first support member for limited oscillation of said arm about a horizontal axis transverse to said arm and with said arm generally horizontally disposed, the other end of said arm including an electrically conductive float supported therefrom electrically connected to the lower end portion of said first support member, the lower end of said second support member being disposed and in vertical registry with said float when said other end of said arm is disposed in its lower limit position and engageable by said float when said other end of said arm is swung upwardly toward is upper limit position, an elongated upstanding tension member having a lower end thereof anchored relative to said arm and the upper end thereof guidingly and shiftably supported from said support means for selective upward displacement relative thereto and including an abutment portion engageable with said support means to limit downward displacement of said tension member relative thereto, the limit of downward displacement of said tension member relative to said support means defining the lower limit of downward movement of the other end of said arm and said float, and electrically actuatable alarm means serially connected in an electrical circuit in which a source of electrical potential as well as said support members are serially connected.