Abstract: A sewer backup alarm and overflow prevention device eliminates raw sewage spills by preventing pressure buildup in sewer drains. One or more sewage level sensors may be coupled to an alarm and/or to an automatic water main shut-off valve. The level sensor may detect excess fluid levels in a sewer lateral line. The sewer backup alarm and overflow prevention device may include a joggle which is a component of a non-mechanical backflow prevention device. The level sensor may detect fluid levels in the lower portion of the joggle and activate the automatic water main shut-off valve and/or the alarm. The sewer backup alarm and overflow prevention device may include at least one two-way, in-line cleanout tube which may extend vertically upwardly from the joggle. The level sensor may be mounted in the vertical cleanout tube. The components may be contained within a seamless polyethylene vault for ease of installation and protection against root intrusion.