House Power Loss Sensor

Wondering if anyone has a simple solution to set up a sensor to detect house power outage/loss?. I am using Konnected Battery Backup and was thinking about installing DC splitter on input side of battery. From there, it seems like a simple 12 vdc NC switch or relay would work. Having trouble locating something that would work.

Any ideas? Thanks.

Btw… I think what I might be looking for is a low power 12vdc reed signal relay.