What's the best detector & alarm for a back flow valve that has been installed by the utility?

Tom Poe Published: March 27, 2020, 6:38 p.m.Last updated: June 17, 2020, 6:19 p.m.

Waste water cannot exit when valve is closed giving a risk of sewage from inside overflowing in basement. Sewer line (Naturally) is below grade and not readily accessible. There is a drain with P trap subject to collecting rain water. It may be a source for detecting sewer backup upon an overflow. What would be the best detector to fit?

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